Cellular radio network reusing frequencies

ABSTRACT

Method of arranging a cellular radio network in a geographical area which is already covered by an existing cellular radio network, wherein cell clusters of the cellular radio network to be introduced and using a specific transmission frequency are located in areas determined by connecting at least two cells of the existing cellular radio network using the specific transmission frequency, and wherein the cell clusters are arranged such that they do not overlap with the cells of the existing cellular radio network. The cell clusters of the introduced cellular radio network may be adjusted by reducing the cell size of cell clusters of the introduced cellular radio network, and by introducing new cells into cell clusters of the introduced cellular radio network. The invention allows to reuse frequencies of an existing cellular radio network by an introduced cellular radio network in the same geographical area.

The invention relates to a cellular radio network and to a method ofarranging a cellular radio network in a geographical area.

TECHNOLOGICAL BACKGROUND OF THE INVENTION

Cellular radio networks are increasingly used to provide a variety ofcommunication and information services to users. In many casescommunication networks coexist with each other in a given geographicalarea and simultaneously provide services to subscribers.

A cellular radio network generally uses a certain partition of theavailable spectrum for providing services. However, as the availablespectrum is limited, the usage of the spectrum is normally subject toregulation and each communication network will have a certain partitionof the spectrum allocated for usage. In this case it needs to be assuredthat the coexisting cellular radio networks, or in general any radionetworks, do not interfere with each other above a certain tolerablelevel.

One straightforward approach to avoid interference between cellularradio networks is to exclusively allocate a certain partition of thespectrum in one geographical area. Each cellular radio network may thenprovide communication services in the allocated partition of thespectrum. Interference may be further reduced by guard bands introducedbetween the allocated partitions of the spectrum.

A frequency range allocated to a cellular radio network may be acontinuous range of frequencies, or certain partitions of the spectrummay be combined to a frequency range for one cellular radio network.Therefore, a frequency range of a cellular radio network may include asingle sequence of frequencies or multiple discontinuous sequences offrequencies, or a set of individual frequencies.

While this approach may work well up to a certain number of subscribersor up to a certain number of networks, in case the number of networks orsubscribers needs to be further increased, the available spectrum maynot suffice for introducing new cellular radio networks or providingservices to further subscribers.

In this case it is desirable to be able to introduce a further cellularradio network in an geographical area already covered by at least onecellular radio network, wherein the introduced cellular radio networkmay reuse frequencies already used in the existing cellular radionetwork.

SUMMARY OF THE INVENTION

It is therefore the object of the invention to provide a cellular radionetwork in a geographical area covered by another cellular radionetwork, wherein both cellular radio networks can provide communicationservices in at least overlapping frequency ranges. Further, it is objectof the invention to reduce interference occurring between the networks.

This object of the invention is solved by the features of claims 1, 16,30 and 39.

A cellular radio network constituting an introduced cellular radionetwork and using a first frequency range, arranged in a geographicalarea served by an existing cellular radio network, the existing cellularradio network using a second frequency range at least overlapping thefirst frequency range, comprises a plurality of cell clusters, each cellcluster including at least one cell, the center of each cell clusterbeing located in a first area defined by connecting at least two cellsof the existing cellular radio network, the at least two cells beingarranged to use the same transmission frequency; and wherein both thecell cluster of the introduced cellular radio network and the at leasttwo cells of the existing cellular radio network are arranged to use thesame transmission frequency.

The invention allows an improved efficiency in using an availablefrequency spectrum in a geographical area served by multiple cellularradio networks. Further, an interference between networks using the sametransmission frequencies in the same geographical area can be reducedand/or a larger number of subscribers may be served.

Advantageously, the center of each cell cluster may be located in thefirst area, the first area being constituted by smallest polygon definedby connecting at least two cells of the existing cellular radio network,and both the cell cluster of the introduced cellular radio network andthe at least two cells of the existing cellular radio network may usethe same transmission frequency.

The first area may be defined by the smallest triangle connecting thecenters of three cells of the existing cellular radio network, the threecells using the same transmission frequency.

The at least two cells of the existing cellular radio network may use atleast one further transmission frequency and the cell cluster of theintroduced cellular radio network may use the at least one furthertransmission frequency.

Further, interference determining means may be provided for receiving avalue indicating an interference from the introduced cellular radionetwork to the existing cellular radio network; and adjusting means maybe provided for reducing the size of at least one cell of at least onecell cluster of the introduced cellular radio network and forintroducing new cells into the at least one cell cluster, if themeasured interference from the introduced cellular radio network to theexisting cellular radio network is larger than a predeterminedthreshold.

Still further, interference determining means may be provided forreceiving a value indicating an interference from the existing cellularradio network to the introduced cellular radio network; and theadjusting means may be arranged for at least one of—to increase atransmission power in the cells of the cell clusters, and—to reduce thesize of at least one cell of at least one cell cluster of the introducedcellular radio network and to introduce new cells into the at least onecell cluster, if the measured interference from the existing cellularradio network to the introduced cellular radio network is larger than apredetermined threshold.

Cells at the periphery of the cluster may use at least one transmissionfrequency within the first frequency range and not within the secondfrequency range.

The cell clusters of the introduced cellular radio network may bearranged such that they do not overlap with cells of the existingcellular radio network which are using the same transmission frequencyas the cell cluster.

Moreover, a first cluster may use a first set of transmissionfrequencies; a second cluster may be located adjacent to the firstcluster may use a second set of transmission frequencies; and the cellsat the periphery of the first cluster may be arranged to use at leastone transmission frequency of the second set of transmission frequenciesand the cells at the periphery of the second cluster may be arranged touse at least one transmission frequency of the first set of transmissionfrequencies and wherein adjacent cells use at least one identicaltransmission frequency.

An apparatus for adjusting cell parameters of cells of a plurality ofcell clusters of a introduced cellular radio network using a firstfrequency range, each cell cluster including at least one cell, theintroduced cellular radio network being arranged in a geographical areaserved by an existing cellular radio network, the existing cellularradio network using a second frequency range at least overlapping thefirst frequency range, comprises: interference determining means forreceiving a value indicating an interference from the introducedcellular radio network to the existing cellular radio network; andadjusting means for adjusting the size of at least one cell of at leastone cell cluster of the introduced cellular radio network and foradjusting the number of cells of the at least one cell cluster independence on the measured interference from the introduced cellularradio network to the existing cellular radio network.

Advantageously, the adjusting means may be adapted to reduce the size ofat least one cell of at least one cell cluster of the introducedcellular radio network and to introduce at least one cell into the atleast one cell cluster, in case the measured interference from theintroduced cellular radio network to the existing cellular radio networkis larger than a first predetermined threshold; and the adjusting meansmay be adapted to increase the size of at least one cell of at least onecell cluster of the introduced cellular radio network and for removingat least one cell from the at least one cell cluster, in case themeasured interference from the introduced cellular radio network to theexisting cellular radio network is smaller than a second predeterminedthreshold.

The interference determining means may be adapted to receive valuesindicating the interference from the introduced cellular radio networkto the existing cellular radio network at a plurality of measurementlocations, and the adjusting means may be adapted to determine at leastone cell cluster causing the measured interference at each measurementlocation and to adjust the determined cell clusters in accordance withthe measured interference.

A method of arranging a introduced cellular radio network using a firstfrequency range in a geographical area served by an existing cellularradio network, the existing cellular radio network using a secondfrequency range at least overlapping the first frequency range,comprises arranging at least one cell of the introduced cellular radionetwork in a cell cluster; determining a first area defined byconnecting at least two cells of the existing cellular radio network,the at least two cells being arranged to use the same transmissionfrequency; arranging the cell cluster in the determined area; whereinboth the cell cluster of the introduced cellular radio network and theat least two cells of the existing cellular radio network are arrangedto use the same transmission frequency.

Another method of adjusting cell parameters of cells of a plurality ofcell clusters of a introduced cellular radio network using a firstfrequency range, each cell cluster including at least one cell, theintroduced cellular radio network being arranged in a geographical areaserved by an existing cellular radio network, the existing cellularradio network using a second frequency range at least overlapping thefirst frequency range, comprises: receiving a value indicating aninterference from the introduced cellular radio network to the existingcellular radio network; and adjusting the size of at least one cell ofat least one cell cluster of the introduced cellular radio network andadjusting the number of cells of the at least one cell cluster dependingon the measured interference from the introduced cellular radio networkto the existing cellular radio network.

The invention may employ the fact that a cellular radio networkservicing a given geographical area does not use the allocated spectrumto its full potential at each and every location in the givengeographical area. The cells of the cellular radio network to beintroduced into a geographical area already served by an existingcellular radio network may advantageously be located such that thefrequencies used by the introduced cellular radio network at aparticular location are not used by the existing cellular radio networkin overlapping cells at the same location.

Thus, the introduced cellular radio network may reuse frequencies of anexisting cellular radio network in the same geographical area.

Further, the invention may advantageously allow to adjust theoperational parameters of the introduced cellular radio network to avoidan interference from the introduced cellular radio network into theexisting cellular radio network above a certain tolerable limit.

According to another example, an introduced or existing cellular radionetwork may be provided, wherein the transmission frequency used by boththe cell cluster of the introduced cellular radio network and the atleast two cells of the existing cellular radio network constitutes afirst transmission frequency; a transmission frequency adjacent to thefirst transmission frequency constitutes a second transmissionfrequency; and a frequency plan used by the existing cellular radionetwork is adapted such that at least one cell of the existing cellularradio network using the second transmission frequency is located at orclose to the center of a second area defined by connecting at least twocells of the existing cellular radio network using the firsttransmission frequency, the first and second area being different fromeach other.

According to another example, an introduced or existing cellular radionetwork may be provided, wherein the transmission frequency used by boththe cell cluster of the introduced cellular radio network and the atleast two cells of the existing cellular radio network constitutes afirst transmission frequency; a transmission frequency adjacent to thefirst transmission frequency constitutes a second transmissionfrequency; and a frequency plan used by the existing cellular radionetwork is adapted such that at least one cell of the existing cellularradio network using the second transmission frequency is dislocated fromthe center of the first area.

According to another example, an introduced or existing cellular radionetwork may be provided, wherein the transmission frequency used by boththe cell cluster of the introduced cellular radio network and the atleast two cells of the existing cellular radio network constitutes afirst transmission frequency; a transmission frequency adjacent to thefirst transmission frequency constitutes a second transmissionfrequency; and wherein the center of a cell cluster of the introducedcellular radio network using the first transmission frequency isdislocated from the center of the first area in a direction increasingthe distance from the cell cluster to the cells of the existing cellularradio network using the second transmission frequency.

According to another example, a cellular radio network may be provided,wherein the transmission frequency used by both the cell cluster of theintroduced cellular radio network and the at least two cells of theexisting cellular radio network constitutes a first transmissionfrequency; a transmission frequency adjacent to the first transmissionfrequency constitutes a second transmission frequency; and wherein thecenter of a cell of the existing cellular radio network is located atthe center of a cell of a cell cluster of the introduced cellular radionetwork using the second transmission frequency.

According to another example, a cellular radio network may be provided,wherein the transmission frequency used by both the cell cluster of theintroduced cellular radio network and the at least two cells of theexisting cellular radio network constitutes a first transmissionfrequency within a first frequency band; a transmission frequencyadjacent to the first transmission frequency constitutes a secondtransmission frequency within a second frequency band; and the at leastone of the first and second transmission frequency is offset from thecenter of the corresponding frequency band in a frequency direction awayfrom the respective other one of the first and second transmissionfrequency.

According to another example, a cellular radio network may be provided,wherein the transmission frequency used by both the cell cluster of theintroduced cellular radio network and the at least two cells of theexisting cellular radio network constitutes a first transmissionfrequency band; an adjacent frequency band is provided, located adjacentto the first transmission frequency band, the adjacent frequency bandincluding a plurality of second transmission frequencies; and whereinthe cell clusters of the introduced cellular radio network and/or the atleast two cells of the existing cellular radio network do not use atleast one of the plurality of second transmission frequencies beinglocated closest to the first transmission frequency band.

Further advantageous features of the invention are recited in furtherclaims.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 a schematically illustrates an introduced cellular radio networkand steps for locating a cell cluster of the introduced cellular radionetwork according to a first embodiment of the invention,

FIG. 1 b schematically illustrates steps for locating a cell cluster ofthe introduced cellular radio network according to another embodiment ofthe invention,

FIG. 1 c schematically illustrates an area for locating a cell clusterof the introduced cellular radio network according to another embodimentof the invention,

FIG. 2 illustrates a cell cluster of the introduced cellular radionetwork according to an embodiment of the invention,

FIG. 3 illustrates an apparatus for locating cell clusters of theintroduced cellular radio network in the same geographical area of anexisting cellular radio network according to an embodiment of theinvention,

FIG. 4 illustrates steps for locating cell clusters of the introducedcellular radio network according to an embodiment of the invention,

FIG. 5 illustrates steps of the method according to another embodimentof the invention,

FIG. 6 illustrates steps according to another embodiment of theinvention for adjusting cell parameters of the introduced cellular radionetwork,

FIG. 7 illustrates steps for adjusting cell parameters according toanother embodiment of the invention,

FIG. 8 illustrates steps of adjusting cell parameters of the introducedcellular radio network according to another embodiment of the invention,

FIG. 9 illustrates an allocation of transmission frequencies accordingto an embodiment of the invention, if the radio channel bandwidth of theexisting cellular radio network is considerably larger than the radiochannel bandwidth of the introduced cellular radio network,

FIG. 10 illustrates steps for adjusting a frequency plan of the existingcellular radio network according to another embodiment of the invention,

FIG. 11 illustrates steps for adjusting a frequency plan of the existingcellular radio network according to another embodiment of the invention,

FIG. 12 illustrates steps for adjusting cell parameters of a cellularradio network according to another embodiment of the invention,

FIG. 13 illustrates steps for adjusting cell parameters of a cellularradio network according to another embodiment of the invention,

FIG. 14 illustrates steps for adjusting frequencies of a cellular radionetwork according to another embodiment of the invention,

FIG. 15 illustrates steps for adjusting frequencies of a cellular radionetwork according to another embodiment of the invention,

FIG. 16 shows an embodiment of the invention illustrating preferredlocations and shapes of cell clusters of an introduced cellular radionetwork, and

FIG. 17 shows an embodiment of the invention illustrating preferredlocations and shapes of cell clusters of an introduced cellular radionetwork.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 a-c schematically illustrate elements of an existing cellularradio network (existing cellular radio network) and elements of anintroduced cellular radio network (introduced cellular radio network)located in the same geographical area. Further, FIGS. 1 a-c illustratesteps performed in locating cell clusters of the introduced cellularradio network into the geographical area.

FIG. 1 a shows an existing cellular radio network 100 comprising aplurality of cells using transmission frequencies A-G of a frequencyrange allocated to the existing cellular radio network, e.g., accordingto a frequency plan as known in the art. In the shown embodiment, theexisting cellular radio network thus has a frequency reuse factor of 7.In the embodiment the cells are shown as hexagons, however, any otherrepresentation of cells may be chosen, such as squares, circles, etc.Further, it is possible that each cell of the existing cellular radionetwork itself constitutes a cell cluster of cells, the cells of therespective cell clusters using the same transmission frequency.

Further, FIG. 1 a shows exemplary portions of an introduced cellularradio network 110, which may be a network to be arranged or rearrangedin the geographical area of the existing cellular network. Theintroduced cellular radio network includes seven exemplary cell clusters115, each cell cluster in this embodiment consisting of a single cell.Each cell cluster of the introduced cellular radio network 110 uses oneof the transmission frequencies A-G. Further, the introduced cellularradio network 110 includes a cell cluster 116 using a frequency C and acell cluster 117 using a transmission frequency A.

Still further, FIG. 1 a illustrates a triangle 111 for locating the cellcluster 116 and a triangle 112 for locating the cell cluster 117 of theintroduced cellular radio network 110.

The triangle 111 has corner points at cells 101, 102 and 103 of theexisting cellular radio network 100, each of the cells 101-103 using atransmission frequency C. The triangle 112 has corner points at cells105, 106 and 107 of the existing cellular radio network 100, each of thecells 105-107 using a transmission frequency A.

The corner point of the triangles may be located in the center of thecells of the existing cellular radio network 100 or at any otherlocation inside the cells of the existing cellular radio network 100.

The introduced cellular radio network 110 preferably uses a firstfrequency range, as exemplary shown in FIG. 1 a a frequency range A-G,and is arranged in a geographical area served by the existing cellularradio network 100, wherein the existing cellular radio networkpreferably has a frequency reuse factor larger than 1 and uses a secondfrequency range, as exemplary shown in FIG. 1 a a frequency range A-G.However, the frequency ranges do not necessarily coincide, they may alsoonly overlap or influence each other.

Further, the introduced cellular radio network 110 includes a pluralityof cell clusters, each of the cell clusters including at least one cell.In the shown embodiment each cell cluster includes one cell. The centerof each cell cluster is preferably located in an area defined byconnecting at least two cells of the existing cellular radio network100. In the present case, the area is constituted by the triangles 111and 112, obtained by connecting three cells of the existing cellularradio network 100. However, it is possible that any other polygon may beused to define the area. The at least two cells of the existing cellularradio network 100 use the same transmission frequency, in the presentcase transmission frequency A, and the cell cluster of the introducedcellular radio network 110, to be located in the defined area, also usesthe transmission frequency A. Thus, both a cell cluster of theintroduced cellular radio network 110 and the at least two cells of theexisting cellular radio network 100 used for defining the area, areusing the same transmission frequency.

As it can be seen in FIG. 1 a, the existing cellular network 100servicing the shown may not fully use the allocated spectrum oftransmission frequencies A-G at each location in the shown area and thecell clusters of the introduced cellular radio network 110 may beadvantageously located such that the frequencies used by cell clustersof the introduced cellular radio network at a particular location arenot used by the existing cellular radio network in cells at thislocation.

In the following, the elements shown in FIG. 1 a are outlined in furtherdetail.

The existing cellular radio network 100 may in general be any cellularradio network having a cell structure for covering a given geographicalarea. For example, the existing cellular radio network 100 may be a GSMnetwork, a wideband CDMA network, a UTRAN network or broadcast network,e.g. a network for television broadcast, video on demand or similar suchas DVB-T or similar. The existing cellular radio network 100 maygenerally have any frequency reuse factor larger than one, i.e. mayreuse frequencies of an allocated set of frequencies according to anygiven scheme. In the shown embodiment the existing cellular radionetwork 100 uses transmission frequencies A-G, i.e. seven frequencies,and therefore is defined to have a frequency reuse factor of 7. However,it is noted that any other frequency reuse factor including a frequencyreuse factor is possible.

The transmission frequencies A-G used by the existing cellular radionetwork 100 and the introduced cellular radio network may be singlefrequencies, however, in practical cases, each of the transmissionfrequencies A-G may include a set of transmission frequencies or rangesof transmission frequencies.

Thus, in the present application, the term transmission frequency is tobe understood as including one or more frequencies. For example, atransmission frequency may include a single carrier frequency and, ifmodulated with the transmission signal, cover a frequency range.Further, even though FIG. 1 a only shows a single layer of cells of theexisting cellular radio network 100, the existing cellular radio network100 may employ multiple layers of cells, e.g. layers of macro cells andlayers of micro cells.

Still further, the person skilled in the art understands that sametransmission frequency is not to be construed as limited tomathematically identical frequencies, rather, the expression “same”transmission frequencies may also include frequencies which aremathematically different but influence each other, e.g. interfere. Thismay also include a transmission frequency which comprises frequencycomponents which are integer multiples of the components of the anothertransmission frequency.

If transmission frequencies each include multiple frequencies or rangesof frequencies, e.g. radio channels, they may be considered toconstitute “same” transmission frequencies, in case frequencies of, e.g.radio channels coincide.

The introduced cellular radio network 110 may be any communicationnetwork, for example, a GSM network, a wideband CDMA network, a UTRANnetwork or broadcast network, e.g. a network for television broadcast,video on demand or similar such as DVB-T or similar. The illustratedexemplary introduced cellular radio network 110 includes a plurality ofcell clusters 115, 116 and 117, each cell cluster using one oftransmission frequencies A-G. Nevertheless, it is possible that theintroduced cellular radio network 110 uses a sub-set of the transmissionfrequencies A-G or additional transmission frequencies, thus, theintroduced cellular radio network 110 may use for example transmissionfrequencies A, B, C, H, K, L. According to the invention, the frequencyranges of the existing cellular radio network and the introducedcellular radio network may only overlap, i.e., that at least somefrequencies are used by both the existing cellular radio network and theintroduced cellular radio network.

In the shown embodiment each cell cluster 115, 116, 117 of theintroduced cellular radio network 110 includes one cell, however, a cellcluster may also include a plurality of cells. A cell cluster 115, 116,117 of the introduced cellular radio network may have a frequency reusefactor of 1 or above. For example, in case each cell cluster has aplurality of cells and the frequency reuse factor is 1, each cell of thecell cluster will use the same transmission frequency.

The cell clusters 115, 116 and 117 of the introduced cellular radionetwork 110 may be located in the same geographical area as the cells ofthe existing cellular radio network 100, however, at locations where theexisting cellular radio network does not use the transmission frequencyof a cluster of the introduced cellular radio network. A cell cluster ofthe introduced cellular radio network is preferably located in an areadefined by connecting at least two cells of the existing cellular radionetwork 100 using the same transmission frequency, while the thusdefined area preferably does not include any further cells of theexisting cellular radio network 100 using the same transmissionfrequency as the transmission frequency of the cells used for definingthe area. The cell cluster of the introduced cellular radio networklocated in the defined area also uses the same transmission frequency,i.e., the transmission frequency of the cells of the existing cellularradio network used for defining the area.

In the example of FIG. 1 a, a triangle 111 defines an area for anexemplary cell cluster 116 of the introduced cellular radio network 110,the cell cluster 116 using the transmission frequency C. The triangle111 is obtained by connecting three cells of the existing cellular radionetwork using the transmission frequency C, in the shown case the threecells 101, 102 and 103 of the existing cellular radio network. The cellcluster 116 is located inside the thus defined area, i.e. triangle 111,and, as it may be taken from FIG. 1 a the cell cluster 116 is nowlocated in a geographical area at which the existing cellular radionetwork does not directly use transmission frequency C.

In general the cell cluster 116 of the introduced cellular radio networkmay be located anywhere inside the area 111, however, it may bepreferred that the cell cluster 116 is arranged inside the area 111 suchthat the cell cluster 116 using transmission frequency C does notoverlap with cells of the existing cellular radio network 100 at thecorner points of the triangle, i.e. cells 101, 102 and 103, also usingtransmission frequency C.

Similarly, a triangle 112 defines an area for an exemplary cell cluster117 of the introduced cellular radio network 110, the cell cluster 117using the transmission frequency A and lying adjacent to cell cluster116. The triangle 112 is obtained by connecting three cells of theexisting cellular radio network using the transmission frequency A, inthe shown case the three cells 105, 106 and 107. The cell cluster 117 islocated inside the thus defined area.

Even though in the present embodiment the adjacent cell clusters 116 and117 have the same size, different sizes for the clusters are possible,e.g. one of the clusters could have a larger radius, e.g. due to systemrequirements, terrain characteristics, subscriber density, interferenceconditions between the introduced cellular radio network and theexisting cellular radio network and similar.

Similar to the cell clusters 116 and 117, the cell clusters 115 andfurther cell clusters may be arranged according to the outlined rules,in order to obtain a full coverage of a given geographical area.

Further, even though in the embodiment described with respect to FIG. 1a the area 111 for locating the cell cluster 116 is a triangle, ingeneral any polygon or shape such as a circle or ellipsoid may beemployed. Preferably, the polygon or shape may be a polygon having agiven number of corners defined by connecting cells of the existingcellular radio network using the same transmission frequency, e.g.transmission frequency A, preferably to avoid that cells of the existingcellular radio network using the transmission frequency of the cellsused for defining the polygon, are located inside the thus defined area.The polygon may be the smallest thus defined polygon of a given numberof cells.

The smallest polygon may be the polygon with the smallest areaconnecting any given number of cells using the same transmissionfrequency.

Even though in FIG. 1 a the existing cellular radio network 110 has afrequency reuse factor of 7, theoretically any other frequency reusefactor is possible, for example frequency reuse factors 3, 4, 9, 12 andsimilar.

As shown in FIG. 1 a, in providing the cell clusters of the introducedcellular radio network at the defined locations, the introduced cellularradio network 110 and the existing cellular radio network 100 maycoexist in a given geographical area while using the same transmissionfrequencies. Since the cell clusters of the introduced cellular radionetwork and the cells of the existing cellular radio network, each usingthe same transmission frequency, are at least not overlapping, or havesome guard space therebetween, particularly an interference from theintroduced cellular radio network to the existing cellular radio networkmay be kept advantageously low. However, also an interference from theexisting to the introduced cellular radio network may be keptadvantageously low.

As an example, the existing cellular radio network may be a broadcastnetwork, and the introduced cellular radio network may be a network forbi-directional communication, such as a GSM network, CDMA network.However, any other combination is possible.

In the following, a further embodiment of the invention will bedescribed with respect to FIG. 1 b, showing an example of locating acell cluster of the introduced cellular radio network.

FIG. 1 b illustrates an existing cellular radio network 150, the cellsof which using frequencies A-L, i.e. the existing cellular radio network150 has a frequency reuse factor of 12. The existing cellular radionetwork 150 may be any cellular radio network for bi-directional oruni-directional communication such as a GSM network, UMTS, broadcastnetwork for video on demand and similar, as outlined before with respectto FIG. 1 a. The existing cellular radio network 150 of the presentexample has a frequency reuse factor of 12, however, this is an exampleonly, any other frequency reuse factor may be present.

Further, FIG. 1 b shows a triangle 160 for locating a cell cluster ofthe introduced cellular radio network using transmission frequency A.The corners of the triangle 160 are located in the centers of cells 151,152 and 153 of the existing cellular radio network 150, the cells usinga transmission frequency A.

In the embodiment of FIG. 1 b an example is shown wherein the area isdefined by the smallest triangle connecting the centers of 3 cells ofthe existing cellular radio network, wherein the cells of the existingcellular radio network are arranged to use the same transmissionfrequency. It is noted, that any other smallest polygon or shape may bedefined connecting at least two cells of the existing cellular radionetwork arranged to use the same transmission frequency, such that nocell of the existing cellular radio network using this transmissionfrequency is located inside the polygon or shape.

Since in the present example the cells of the existing cellular radionetwork 150 are arranged regularly, in the shown example the triangle isan equilateral triangle. In practical scenarios, however, the obtainedtriangle may not necessarily be equilateral, e.g., due to terraincharacteristics, subscriber density and similar.

Further, in the shown embodiment of FIG. 1 b it may be preferred that acell cluster of the introduced cellular radio network is located in thedefined area. Further, it may also be preferred that the center of thecell cluster of the introduced cellular radio network is located at thecenter of the defined area, i.e. in the present embodiment located atthe center 163 of the triangle 160, such that the distance between thecells of the existing cellular radio network used for obtaining the areaand the cell cluster is as large as possible. Thus, the distance betweencells and cell clusters using the same transmission frequency may beadvantageously large, in the present case between cells 151, 152 and 153using the transmission frequency A and a cell cluster using thetransmission frequency A located at the center 163. In this case aninterference between the introduced cellular radio network and theexisting cellular radio network may be kept low.

In case the triangle 160 is an equilateral triangle as in the presentcase, the center 163 may be obtained by determining the intersection oflines 161 and 162, the lines 161 and 162 being lines vertical to thecorresponding sides of the triangle 160, intersecting the correspondingsides of the triangle 160 at their midpoint. However, it is alsopossible that instead a center of gravity or any other location insidethe triangle 160 is determined, e.g. allowing reduced interferencebetween the existing and introduced cellular radio network.

Even though the location of a single cell cluster of the introducedcellular radio network having transmission frequency A is illustrated,any other cell cluster of the introduced cellular radio network may belocated at similar locations, determined by triangles connecting threecells of the existing cellular radio network using the same transmissionfrequency, e.g. three cells using transmission frequency B, three cellsusing transmission frequency C, etc.

Even though the existing cellular radio network 150 and the introducedcellular radio network 110 may use the same set of transmissionfrequencies, it is also possible that only some frequencies are at thesame time used by the existing cellular radio network and the introducedcellular radio network. It is further possible that the cells of theexisting cellular radio network, used for determining the corner pointsof the triangle 160 are using at least one further transmissionfrequency and the cell cluster of the introduced cellular radio network,i.e. the cell cluster located at the center 163 also uses the at leastone further transmission frequency. As already outlined with respect tothe embodiment of FIG. 1 a, locating cell clusters as outlined above maykeep an interference advantageously low.

In the following, a further embodiment of the invention will bedescribed with respect to FIG. 1 c. FIG. 1 c shows a further example ofareas defined for locating cell clusters of the introduced cellularradio network.

FIG. 1 c shows an exemplary existing cellular radio network 170 having afrequency reuse factor of 12 and using transmission frequencies A-L. Theexisting cellular radio network may be a cellular radio network asoutlined with respect to the previous embodiments.

Further, FIG. 1 c shows an area 181 determined by connecting two cells171 and 172 using a transmission frequency A of the existing cellularradio network 170. Even though the area 181 could be drawn as a singleline, e.g., a line connecting the centers of cells 171 and 172 of theexisting cellular radio network 170, the area 181 is drawn having acertain width determined by the width of the cells 171 and 172 orsimilar. Further, FIG. 1 c shows a similar area 183 determined byconnecting two cells 173 and 174 using a transmission frequency C of theexisting cellular radio network 170. Still further, FIG. 1 c shows acell cluster 180 of the introduced cellular radio network, such as thecellular radio network 110 described with respect to FIG. 1 a, the cellcluster using a transmission frequency A and the center of the cellcluster 180 being located in the area 181, and, FIG. 1 c shows a cellcluster 182 using a transmission frequency C located in the area 183.

Thus, as in the previous embodiments, the cell cluster 180 is located inan area which is defined by connecting a plurality of cells of theexisting cellular radio network, in the present case two cells 171 and172 of the existing cellular radio network, wherein the cells of theexisting cellular radio network used for defining the areas and therespective cell cluster of the introduced cellular radio network use thesame transmission frequency, e.g. the cells 171 and 172 used fordefining the area 181 and the cell cluster 180 use the same transmissionfrequency, in the present case transmission frequency A.

Even though the cell cluster 180 may be located generally anywherewithin the area 181, it may be preferred that the cell cluster 180 islocated in the middle of the area 181, such that the distance betweenthe cell cluster 180 and the cells 171 and 172 of the existing cellularradio network are identical, in order to achieve improved performance,i.e. reduced interference. The same applies to cell cluster 182.

The size of the cell clusters may be chosen such that a seamlesscoverage is possible, as in the present case. Since the size of the cellclusters in the present example is exemplarily shown larger than thesize of the cells of the existing cellular radio network, a sub-set ofthe transmission frequencies A-L of the existing cellular radio networkwill suffice in this case for establishing the introduced cellular radionetwork.

Even though only two cell clusters 181 and 183 of the introducedcellular radio network are illustrated, it is understood that all cellclusters of the introduced cellular radio network may be similarlylocated, e.g. in the area of the smallest polygon defined by connectingat least two cells of the existing cellular radio network, using thesame transmission frequency. According to the invention, the introducedcellular radio network may provide full geographical coverage, as thecell clusters may be arranged contiguously with one another.

In the following, a further embodiment of the invention will bedescribed with respect to FIG. 2.

FIG. 2 shows an example of a cell cluster 200 of an introduced cellularradio network, e.g. the introduced cellular radio network 110 describedwith respect to the embodiment of FIG. 1 a. The cell cluster 200 of FIG.2 is assumed to include seven cells with reference numeral 210 using atransmission frequency A, i.e., the cell cluster 200 of FIG. 2 isassumed to have a frequency reuse factor of 1.

Even though the cell cluster 200 is shown to include seven cells 210,any other number of cells is possible and may also be altered duringoperation of the network.

Even though not illustrated, at least one of the cells 210 of the cellcluster 200 may itself be constituted by cell clusters.

The size of the cell cluster 200 may preferably be chosen such that cellclusters of an introduced cellular radio network are arrangedcontiguously with each other and thus cover a given geographical areawithout gaps. Further, the size of the cells of the cell cluster may bedifferent, e.g. larger cells may be placed into the center of the cellcluster.

The number of cells of the introduced cellular radio network may bevaried in accordance with an interference of the introduced cellularradio network with the existing cellular radio network, i.e. aninterference introduced in the existing cellular radio network throughthe operation of the introduced cellular radio network. Since thetransmission power required in a cellular radio network among otherfactors depends on the size of a cell, a transmission power can bereduced by reducing the cell size of the cell cluster 200 of theintroduced cellular radio network. Thus, if for example an interferencemeasured at a given location in the existing cellular radio network ishigh, caused by the introduced cellular radio network, the cell size ofthe cells of a cluster of the introduced cellular radio network may bereduced, and, in order to still fully cover a given geographical area,new cells may be included into the cell clusters.

Further, in case the measured interference of the introduced cellularradio network to the existing cellular radio network is lowered, theprocess may be reverted and the cell size of the cells of the cellclusters may be increased.

The size of the cell cluster 200 may be chosen such that a contiguousarea may be covered by the introduced cellular radio network, however,the size of the cell clusters of the introduced cellular radio networkat different locations may vary according to circumstances, e.g. terraincharacteristics, subscriber density and similar. It may be preferredthat the cell size of the introduced cellular radio network is limitedsuch that the cell clusters do not overlap with cells of the existingcellular radio network using the same transmission frequency as the cellcluster.

Even though the cell cluster illustrated in FIG. 2 is shown to have afrequency reuse factor of 1, any other frequency reuse factor may beused. However, it should be ensured that a frequency of the introducedcellular radio network is not already used by the existing cellularradio network at the same location.

Moreover, cells at the periphery of the cluster may use a transmissionfrequency within the frequency range assigned to the introduced cellularradio network and not within the frequency range of the existingcellular radio network, in order to further reduce the interferencebetween the networks.

Further, the size of a cell cluster of the introduced cellular radionetwork may be equal to the average size of the cells of the existingcellular radio network used for obtaining the area for locating the cellcluster.

Finally, cell size of a cell at the periphery of a cluster of theintroduced cellular radio network may be smaller than the cell size of acell at the center of the cell cluster.

In the following a further embodiment of the invention will be describedwith respect to FIG. 3. FIG. 3 partially shows an example of anintroduced cellular radio network 300, e.g. as outlined before. Theintroduced cellular radio network includes a plurality of cell clusters301, each using at least one of the transmission frequencies A-G andhaving a plurality of cells. The cell clusters may be arranged asdescribed with respect to the previous embodiments.

An existing cellular radio network, e.g. as outlined with respect toprevious embodiments, is denoted with reference numeral 320, andcoexists with the introduced cellular radio network in the samegeographical area.

FIG. 3 further shows control means 310 for dynamically adjustingcharacteristics of the introduced cellular radio network. The controlmeans 310 includes interference measuring means 311 and adjusting means312 for adjusting cell clusters. An arrow 314 illustrates controlinformation exchanged between the cellular radio networks and thecontrol means 310.

The introduced cellular radio network 300 is illustrated with seven cellclusters 301, each cell cluster being constituted by seven cells. Eachof the shown cell clusters uses one of the frequencies A-G. Further, thefrequencies A-G are also used by the existing cellular radio network320. However, this is an example only, any other scenario is possible,as outlined before.

The exemplary cell clusters of the introduced cellular radio network 300have a frequency reuse factor of 1, indicating that the cells of eachcell cluster use the same transmission frequency. However, as outlinedwith respect to previous embodiments, it is also possible that frequencyreuse factors larger than 1 may be employed for cell clusters of theintroduced cellular radio network. The cell clusters of the introducedcellular radio network may be arranged as it was outlined with respectto previous embodiments, i.e., each cell cluster is located in an areadefined by connecting at least two cells of the existing cellular radionetwork 320, wherein the at least two cells of the existing cellularradio network are arranged to use the same transmission frequency, whichis the transmission frequency also used by the cell cluster arranged inthe thus defined area.

The control means 310 is provided for dynamically adjusting parametersof the introduced cellular radio network, in order to maintain a propercoexistence between the existing cellular radio network and theintroduced cellular radio network. The control means is arranged toadjust parameters of the introduced cellular radio network in order tomaintain an interference from the introduced cellular radio network intothe existing cellular radio network below a certain acceptable level.The acceptable level may be defined by the operator of the existingcellular radio network or may be a limit self-imposed by the operator ofthe introduced cellular radio network or may be a limit imposed byregulating authorities.

If for example an interference from the introduced cellular radionetwork in the existing cellular radio network, i.e. an interferencemeasured in the existing cellular radio network, caused by theintroduced cellular radio network, is above the acceptable limit, theparameters of the introduced cellular radio network may be adjusted suchthat the interference is reduced below the acceptable level. Likewise,in case the interference measured in the existing cellular radio networkis decreased, the parameters of the introduced cellular radio networkmay be adapted, as explained below, such that interference is increasedbut does not exceed the acceptable limit.

It may be preferred that an interference in the existing cellular radionetwork, caused by the introduced cellular radio network, is measured ata plurality of locations, and that the parameters of the introducedcellular radio network are locally adapted to the measured interferencelevel, i.e., the introduced cellular radio network may be locallyadapted to interference conditions.

For example, an interference could be measured at statisticallyrepresentative positions in the existing cellular radio network, forexample located at base stations or mobile stations, determinedaccording to subscriber density, terrain characteristics and similar.Thus, the interference may be measured on the downlink transmission pathand on the uplink transmission path.

The control means 310 may be constituted by a data processing unit or aplurality of data processing units communicating via a network or viadedicated communication links.

The control means 310 includes the interference measuring means 311, atleast for measuring the interference in the existing cellular radionetwork caused by the introduced cellular radio network. It is alsopossible that the control means only includes means for receiving valuesindicating an interference caused by the introduced cellular radionetwork. These interference measurements may for example be provided bythe operator of the existing cellular radio network, e.g. using basestations and measurements on communication links. The control means 310further includes means for adjusting the parameters of the introducedcellular radio network, e.g., for adjusting parameters of the cellclusters of the introduced cellular radio network. The cell parametersto be adjusted may be at least one of:

-   -   the number of cells included in a cell cluster,    -   the cell size of a cell of a cell cluster,    -   a maximum number of subscribers, and    -   the transmission power used for transmissions in a cell of a        cell cluster of the introduced cellular radio network,        and similar.

The transmission power in a cell of a cell cluster of the introducedcellular radio network may depend on terrain characteristics, a numberof subscribers, and similar. Further, it may be preferred that theadjusting means 312 for adjusting cell clusters is adapted to locallyadjust the parameters of the cell clusters of the introduced cellularradio network in accordance with the interference measurements obtained.Thus, the adjusting means may be used to locally adjust thecharacteristics of the introduced cellular radio network. Thus, theadjusting means may reduce the size of at least one cell of at least onecell cluster of the introduced cellular radio network and/or introducenew cells into the at least one cell cluster, in case the measuredinterference from the introduced cellular radio network to the existingcellular radio network or the interference from the existing cellularradio network to the introduced cellular ratio network is larger than apredetermined threshold.

Still further, the adjusting means 312 for adjusting cell clusters maybe arranged to determine cell clusters which are actually causing themeasured interference at each measurement location and may be arrangedto adjust the determined cell clusters in accordance with the measuredinterference, as outlined before. This may, for example, be achieved bydetermining the cell clusters in the neighborhood of the measurementlocation likely to cause interference. Further, by determining whichtransmission frequencies cause the interference, cell clusters causinginterference may be identified.

For example, in case in a given local area the measured interferencefrom the introduced cellular radio network to the existing cellularradio network is above a certain limit, the cell site density of atleast one cell cluster in an area the interference measurement isrepresentative for, could be adjusted accordingly. For example, a cellradius could be decreased and in order to maintain the size of the cellcluster or full geographical coverage, new cells could be introducedinto a cell cluster.

Further, the size of a cell cluster could be reduced and/or further cellclusters could be introduced or neighboring cell clusters could beincreased in size. Also, an allowed maximum number of subscribers in acell cluster could be reduced, in order to reduce the transmission powerin a cell cluster, or further frequencies of a frequency range allocatedfor the introduced cellular radio network could be introduced into cellclusters, e.g., by introducing cells using further transmissionfrequencies.

In a further embodiment of the invention the interference measuringmeans may further include means for measuring the interference from theexisting cellular radio network to the introduced cellular radionetwork, e.g. at statistically representative locations, as outlinedbefore. The interference measurements of an interference in theintroduced cellular radio network caused by the existing cellular radionetwork may be used to further adapt the characteristics of theintroduced cellular radio network. For example, in case the interferencefrom the existing cellular radio network to the introduced cellularradio network is above a certain threshold, meaning that operations ofthe introduced cellular radio network are deteriorated, a transmit powerin the introduced cellular radio network may be adjusted so that adesired distribution of carrier to interference ratios is achieved inthe introduced cellular radio network. Further, means may be providedfor measuring a propagation attenuation from the positions ofmeasurement of an interference from the existing cellular radio networkto the introduced cellular radio network, e.g. to a serving base stationof the introduced cellular radio network.

Further, it is possible that different thresholds are defined, e.g., anupper threshold for a maximum acceptable interference from theintroduced cellular radio network to the existing cellular radio networkis defined, and that a lower threshold for the interference from theintroduced cellular radio network to the existing cellular radio networkis defined. In case the interference measured is above the upperthreshold, the parameters of the introduced cellular radio network maybe adjusted such that the interference is below the upper threshold.

In order to avoid a continuous control operation, the parameters of theintroduced cellular radio network are only adjusted, if the measuredinterference decreases below the lower threshold, in which case theparameters of the introduced cellular radio network are adjusted suchthat the interference slightly rises. The thus introduced hysteresisavoids a permanent control operation, control operations may only beperformed, if the measured interference is above the upper threshold orbelow the lower threshold. It is noted that the described hysteresis maybe applied in both cases, i.e., in case the interference from theintroduced cellular radio network to the existing cellular radio networkis measured, and in case the interference from the existing cellularradio network to the introduced cellular radio network is measured.

It is noted that a computer readable medium may be provided having aprogram recorded thereon, where the program is to make a computer orsystem of data processing devices execute functions of the abovedescribed elements. A computer readable medium can be a magnetic oroptical or other tangible medium on which a program is recorded, but canalso be a signal, e.g. analog or digital, electromagnetic or optical, inwhich the program is embodied for transmission.

Further, a computer program product may be provided comprising thecomputer readable medium.

In the following a further embodiment of the invention will be describedwith respect to FIG. 4. FIG. 4 shows a sequence of steps performed forarranging or re-arranging cell clusters of the introduced cellular radionetwork in a given geographical area which is already covered by anexisting cellular radio network, for example as performed by the controlmeans described with respect to FIG. 3.

In a first step S401 an area is determined by connecting at least twocells of the existing cellular radio network, the at least two cellsusing the same transmission frequency. In case two cells of the existingcellular radio network are connected, a corridor may be defined, e.g.determined by the width of the cells of the existing cellular radionetwork. In case the area is determined by connecting three cells of theexisting cellular radio network, a triangle is obtained, whichpreferably does not cover any other cells of the existing cellular radionetwork using the transmission frequency of the cells used for definingthe triangle, i.e. cells at the corners of the triangle. Further, fouror more cells of the existing cellular radio network may be used todetermine the area.

In the following, in a step S402 at least one cell of the cellular radionetwork to be introduced is arranged in a cell cluster, and in a stepS403 the center of the cell cluster is located in the area determined instep S401.

As outlined with respect to previous embodiments, the cell cluster to belocated in the determined area will be arranged to use the sametransmission frequency as the cells of the existing cellular radionetwork used for determining the area.

In step S402 the number of cells of the cell cluster to be introducedinto the area may be determined in accordance with interferencemeasurements or estimated interference from the cell cluster of thecellular radio network to be introduced to the cells of the existingcellular radio network. As the interference will depend on the size ofthe cells of the cell cluster, in case the interference is high, alarger number of cells may be arranged in a cell cluster. Further, thenumber of cells in a cell cluster may also be determined by the numberof subscribers, terrain characteristics and similar.

For the dimensioning of the transmit power and the cell size of thecells of the cell cluster, the dependency between the cumulative poweremitted from the cell cluster of the introduced cellular radio networkand the cell size of a cluster of the introduced cellular radio networkmay be used, as it may be derived as follows.

The propagation attenuation L, e.g. of a base station of the introducedcellular radio network versus distance d to a transmitter, e.g. of abase station may be assumed to be of Okumura Hata type, as described inHata Masahura “Empirical Formula for Propagation Loss in Land MobileRadio. Services”, IEEE Transactions on Vehicular Technology, Vol. VT-29,No. 3, pp. 317-325, August 1980 with parameters L_(0,2) and ξ₂:L=L _(0,2) ·d ^(ξ2)  Eq. 1wherein L_(0,2) and ^(ξ2) depend on parameters as the frequency and usedantenna, terrain characteristics and similar.

The transmit power P required in one cell of the cell cluster depends onthe radius r₂ as follows:P=f(k)·r ₂ ^(ξ) ²   Eq. 2wherein r₂ is the radius of a cell of a cell cluster and k is the numberof users in the cell of the cell cluster. f(k) is a non decreasingfunction of k. For example, if the transmit power P is independent ofthe number of users (as it is the case for broadcast systems) thenf(k)=c with c being a constant.

For equation 2 it is assumed that the cell has a circular border andthat the base station is located at the center of the circle. It isfurthermore assumed that the users are randomly distributed in the cellwith uniform distribution.

The transmit power P is an average power over dimensions time t, user uand user distribution z.

P (z, u, t) is denoted the power used for a given user distribution z ata time t for a user u. P (z, u, t) may be the power used by the mobilestation of the user, when the uplink connection from the user to thebase station is considered, or it may be the power used by the basestation for the connection to the mobile station of the user, if thedownlink is considered.

The function f(k) depends on the radio access technology of theintroduced cellular radio network.

For system like UTRAN with user individual transmit power control thatregulates the carrier to interference ratio at the user to a constant(possibly user individual) target, f(k) approaches a positive minimalvalue a for k→0 (a>0 is caused by the power required for broadcastcontrol channels) and the first and second derivative of f(k) ispositive, as outlined in Kimmo Hiltunen, Riccardo de Bernardi: WCDMAcapacity estimation; VTC 2000 spring, pages 992-996, May 2000, Tokyo,Japan. However, this is an example only.

For these systems, f(k) may also increase with the interference floorcaused from the existing cellular radio network to the introducedcellular radio network, and thus the interference from the existingcellular radio network to the introduced cellular radio networkinfluences P.

The number of users in a hexagonal cell of the introduced cellular radionetwork depends on the given user density U and on r₂ as follows:$\begin{matrix}{k = {\frac{3 \cdot \sqrt{3}}{2}{U \cdot r_{2}^{2}}}} & {{Eq}.\quad 3}\end{matrix}$and, in case the size of a cell cluster is equal to the size of a cellof the existing cellular radio network, the number N of cells per cellcluster of the introduced cellular radio network depends on r₂ and thecell radius r₁ of the cells of the existing cellular radio network:$\begin{matrix}{N = \frac{r_{1}^{2}}{r_{2}^{2}}} & {{Eq}.\quad 4}\end{matrix}$

Finally, the cumulative transmit power of all N cells of a cell clusterof the introduced cellular radio network may be written as:$\begin{matrix}{P_{tot} = \frac{r_{1}^{2} \cdot {f\left( {\frac{3 \cdot \sqrt{3}}{2}{U \cdot r_{2}^{2}}} \right)} \cdot r_{2}^{\xi_{1}}}{r_{2}^{2}}} & {{Eq}.\quad 5}\end{matrix}$

As ξ_(s)>2 and f(k)→a for k→0 follows P_(tot)→0 for r₂→0. This meansthat the interference from the introduced cellular radio network to theexisting cellular radio network can be made arbitrarily small fordecreasing r₂.

As P_(tot) must be limited in order to avoid excessive interference fromthe introduced cellular radio network to the existing cellular radionetwork, the cell radius r₂ should be adapted accordingly. The limit onthe largest acceptable P_(tot) may be determined by the propagationattenuation from the cell cluster of the introduced cellular radionetwork to a cell of the existing cellular radio network using the samefrequency and by a tolerable interference from the introduced cellularradio network to the existing cellular radio network.

Thus, in step S402 the cell cluster parameters, as cell size, transmitpower etc., may be determined or adjusted. The adaptation of thetransmit power and the cell site density of the introduced cell cluster,i.e. the number of cells of the introduced cell cluster and its size hasto be performed in dependency on each other. An increase of the numberof cells allows a decrease of the transmit power and enables a decreaseof the cumulative power that emits from the cell cluster. The cumulativepower of a cell cluster determines the interference caused to theexisting cellular radio network. The cell site density will preferablybe set to the smallest value for which the interference is stillacceptable.

While it may be preferred that the cell cluster uses one transmissionfrequency, i.e. should be designed for a frequency reuse factor 1 ormust at least be able to achieve acceptable performance for this reusefactor, larger reuse factors for the cell cluster are possible. In thiscase for each frequency it could be decided separately if it can be usedin the cluster, i.e., whether it fulfils the above-stated requirements.

Steps S401, S402 and S403 may be repeated for a plurality of cellclusters of the introduced cellular radio network to be arrangedadjacent to one another in order to obtain a full coverage of a givengeographical area. Preferably the size of a cell cluster also depends onan overall number of cell clusters to be introduced and their size. Itmay be desirable to adjust the size of a cell cluster approximatelyequal to the size of a cell of the existing cellular radio network, inwhich case an even distribution of cell clusters may be achieved.

It is noted that a plurality of cellular radio networks may be arrangedaccording to the described method, i.e., the cellular radio networkreferred to as existing cellular radio network may already be a cellularradio network introduced into another existing cellular radio network.

In the following, a further embodiment of the invention will bedescribed with respect to FIG. 5. FIG. 5 outlines a sequence of stepsfor arranging or re-arranging a number of cell clusters of the cellularradio network to be introduced in a geographical area which is alreadycovered by an existing cellular radio network.

In a first step S501 the center of an area of a smallest polygonobtained by connecting at least two cells of the existing cellular radionetwork with the same transmission frequency is determined.

In case two cells of the existing cellular radio network are used fordetermining the polygon or shape, the center may be a location atmidpoint between the two cells used for defining the polygon. In casefor example three cells using the same transmission frequency of theexisting cellular radio network are used for determining the polygon orshape, a triangle will be obtained, which, in case the cells of theexisting cellular radio network are evenly distributed, will beequilateral. The requirement of the smallest polygon or shape connectingcells using the same transmission frequency assures that no other cellsof the existing cellular radio network using the transmission frequencyof cells used for determining the polygon are located inside the area ofthe polygon or shape. The requirement of determining the center assuresthat the distance from the center to the cells of the existing cellularradio network at the corner points of the polygon is as large aspossible for all used cells of the existing cellular radio network.

Instead of the center of the polygon it is also possible that a centerof gravity of the polygon is determined, or any other point in the areaof the polygon allowing a large distance between the determined pointand the cells at the corner points of the polygon. Any other pointinside the area may be defined which provides a good tradeoff betweenthe obtained distances between the determined point and the cells at thecorners of the polygon.

In a step S502 the center of a cell cluster using the same transmissionfrequency as the cells used for determining the polygon is located atthe point inside the area determined in step S501, e.g., the center ofthe area of the polygon, the center of gravity or similar.

It is noted that in practical cases according to terraincharacteristics, subscriber densities and similar the center of the cellcluster may not always be located exactly at the determined point insidethe polygon, the described rules are rather to be considered asguidelines for locating cell clusters.

In a step S503 the size of the introduced cell cluster is adjusted suchthat it preferably does not overlap with cells of the existing cellularradio network at the corner points of the polygon which are using thesame transmission frequency as the cell cluster. While this determines apreferred maximum size of a cell cluster, a practical size of a cellcluster may be chosen smaller than the defined rule, e.g., within therange of the sizes of the cells of the existing cellular radio network.

In a step S504 the above steps S501-S503 are repeated in order toarrange a plurality of cell cluster adjacent to each other for entirelycovering the given geographical area.

The described method allows to arrange cell clusters containing at leastone cell of the introduced cellular radio network in a geographical areawhich is already covered by cells of an existing cellular radio networkwhile avoiding an interference between the cellular radio networks to bemaintained at a tolerable level. The cell clusters, i.e., the cell sitedensity, transmission power and similar may be adjusted, as outlinedbefore with respect to the embodiment of FIG. 4.

In the following, a further embodiment of the invention will bedescribed with respect to FIG. 6. FIG. 6 describes in further detail amethod to adjust the cell clusters of the introduced cellular radionetwork in order to maintain an overall interference between thecellular radio networks within a tolerable level. The steps outlinedwith respect to FIG. 6 may be performed during arranging the cellclusters, i.e., during establishing the cellular radio network to beintroduced, or may be used in adjusting the cell clusters of theintroduced cellular radio network to changing requirements, e.g. in casethe existing cellular radio network is changed by altered circumstancessuch as user density, environmental changes such as buildings andsimilar. The steps may be performed, for example by the control meansdescribed with respect to FIG. 3.

Further, the steps may be used to adjust the introduced cellular radionetwork in case conditions of the introduced cellular radio networkchange, e.g. subscriber number, terrain changes as before and similar.

In a first step S601 the interference from the introduced cellular radionetwork to the existing cellular radio network is measured, preferablyat selected locations, e.g. defined by base stations or selectedaccording to statistical considerations. The interference may bemeasured at the selected locations by the operator of the existingcellular radio network or by any other entity and may be provided to theoperator of the introduced cellular radio network.

In a step S602 it is preferably determined which cell clusters actuallycause the measured interference, measured in step S601, i.e., which cellclusters of the introduced cellular radio network are responsible forthe interference measured at at least one selected location. This may befor example a number of cell clusters in the vicinity of the measurementlocation, e.g. cell clusters using a particular frequency or similar.

In a step S603 the size of the cells of the cell clusters determined instep S602 may be reduced and/or new cells may be introduced into thecell clusters of the introduced cellular radio network, in order tomaintain a full coverage of the given geographical area. Further, it ispossible that the size of a particular cell cluster is reduced, andfurther cell clusters are introduced or neighboring cell clusters areincreased in size, according to further interference measurements.

An increased interference may be due to increased numbers of subscribersin one or both of the existing cellular radio network and introducedcellular radio network, or may be due to terrain changes or otherconditions such as weather, subscriber activity and similar.

Steps S601-S603 may be repeated for a larger number of locations, ifnecessary, in order to adjust all areas of the introduced cellular radionetwork according to interference measurements. The threshold for theinterference may be set by an operator of the existing cellular radionetwork, by a regulating authority or may be self-imposed by theoperator of the introduced cellular radio network.

In the following a further embodiment of the invention will be describedwith respect to FIG. 7. FIG. 7 shows a sequence of steps of adjustingthe cell clusters of the introduced cellular radio network, e.g., in aparticular area determined to influence an interference measurementtaken at a selected geographical location.

In a first step S701 the interference from the introduced cellular radionetwork to the existing cellular radio network is measured, e.g. at aselected location, as outlined with respect to previous embodiments.

In a step S702 it is determined whether the measured interference islarger than a threshold and if the decision in step S702 is “yes”, in astep S703 the cell site density of clusters of the introduced cellularradio network is increased, i.e., new cells may be introduced into thecell clusters and/or the cell size of the cells of the cell clusters maybe reduced. Since this may cause a reduced transmit power of the cellsand an reduced overall transmit power of the cell cluster, step S703 mayreduce the interference measured.

In case the decision in step S702 is “no”, in a step S704 the cell sitedensity of the cell clusters of the introduced cellular radio network isdecreased, e.g., cells may be removed from cell clusters and/or atransmit power may be increased in order to increase the radius of acell of the cell cluster.

Following to step S703 and S704 the flow returns to step S701, and theadjustment step is repeated. The steps outlined with respect to FIG. 7may be repeated for a plurality of selected geographical locations, asoutlined before.

The adaptation process described in FIG. 7 allows to maintain theinterference from the introduced cellular radio network to the existingcellular radio network around the level of the defined threshold andthus allows to maintain proper operation of both networks.

The introduced cellular radio network may be designed to employ macrodiversity techniques. However in this case there is the drawback thatfurther borders between cells of the introduced cellular radio networkare established that use different frequencies. Applying macro diversitywith different frequencies may be implemented using two separatereceivers, which, however, is expensive.

In a further advantageous embodiment the invention allows to introducemacro diversity at reduced costs.

The distance from a cell border, within which macro diversity iseffective, depends on the cell size and consequently the size of theborder areas lacking macro diversity are reduced with the cell size ofthe cell clusters. However, cells may not be arbitrarily small.

Therefore, according to this embodiment of the invention, in a cellcluster using a frequency group X the border cells may use one frequencyof a frequency group Y, which is a frequency group used by an adjacentcell cluster, as a replacement for one frequency of the frequency groupX. The same may be applied for all cells of cell clusters at bordersbetween two cell clusters using any other pair of frequency groups thanX and Y.

Accordingly, a first cluster may be arranged to use a first set oftransmission frequencies, and a second cluster located adjacent to thefirst cluster may be arranged to use a second set of frequencies. And atleast one cell at the periphery of the first cell cluster may bearranged to use at least one transmission frequency of the second set oftransmission frequency and at least one cell at the periphery of thesecond cell cluster may be arranged to use at least one transmissionfrequency of the first set of transmission frequencies and adjacentcells may use at least one identical transmission frequency.

It is noted that the method steps for locating and adjusting the cellclusters of the introduced cellular radio network as well as steps formeasuring an interference may be implemented by programs including codedinstructions for execution on a data processing unit or a plurality ofdata processing units connected by a network or by dedicatedcommunication links.

In the following a further embodiment of the invention will be describedwith respect to FIG. 8. FIG. 8 describes a further sequence of steps forarranging and/or adjusting cell clusters of the introduced cellularradio network to an existing cellular radio network in a givengeographical area.

In a first step S801 the interference from the introduced cellular radionetwork to the existing cellular radio network is measured, e.g. at aselected location, as outlined before.

In a step S802 it is determined whether the measured interference islarger than a predefined upper threshold, e.g. defined as outlinedbefore by the operators of the networks or a regulating authority.

In case in step S802 the decision is “yes” in a step S803 the size ofcells of the cell clusters of the introduced cellular radio network maybe reduced and/or a transmit power may be reduced. The cell clusters tobe adjusted according to step S803 may be determined beforehand, e.g.,cell clusters which cause the measured interference, e.g., cell clustersin the vicinity of a measurement location for measuring interferenceand/or cell clusters using specific frequencies in a particular area.

In a step S804, since the size of the cells of the cell clusters arereduced, new cells are introduced into the cell clusters, in order tomaintain four geographical coverage.

In case in step S802 the decision is “no”, in a step S805 it isdetermined whether the interference is below a lower determinedthreshold, e.g. defined as before.

In case in step S805 the decision is “no”, the flow returns to stepS801.

In case in step S805 the decision is “yes”, in a step S806 the size ofthe cells of the cell clusters is increased and/or the transmit power isincreased. The cell clusters may be determined as outlined with respectto step S803.

In the following, in a step S807 cells from the cell clusters of theintroduced cellular radio network are removed, as after increasing thesize of cells a reduced number of cells is necessary for full coverageof a geographical area.

After steps S804 and S807 in a step S808 the interference from theexisting cellular radio network to the introduced cellular radio networkmay be measured and a propagation attenuation at selected locations fromthe measurement positions to serving base stations of the introducedcellular radio network may be measured. In a step S809 the transmitpower in the introduced cellular radio network may be adapted inaccordance with the measurements of step S808.

Interference determining means may be provided for receiving a valueindicating an interference and from the existing cellular radio networkto the introduced cellular radio network; and the adjusting means mayreduce the size of at least one cell of at least one cell cluster of theintroduced cellular radio network and introduce new cells into the atleast one cell cluster, in case the measured interference from theexisting cellular radio network to the introduced cellular radio networkis larger than a predetermined threshold. The adjusting means mayfurther increase the size of at least one cell of at least one cellclusters and remove at least one cell from at least one cell cluster ofthe introduced cellular radio network, in case the measured interferencefrom the existing cellular radio network to the introduced cellularradio network is smaller than another predetermined threshold.

It is, however, noted that steps S808 and S809 may be optional. Afterstep S809 the flow returns to step S801.

The method steps outlined with respect to FIG. 8 allow to adjust theintroduced cellular radio network to meet interference requirements,while avoiding a continuous adaptation process by introducing ahysteresis between the upper and lower defined threshold. In case theinterference is between the upper and lower threshold, no adaptationstep is required, reducing operational costs. Further, the stepsdescribed in FIG. 8, particularly steps S808 and S809 allow to adjustthe cell clusters of the introduced cellular radio network tointerference measurements of an interference from the existing cellularradio network to the introduced cellular radio network, in order toavoid deteriorated operation of the introduced cellular radio network.

It is noted that a computer readable medium may be provided having aprogram recorded thereon, where the program is to make a computer orsystem of data processing devices execute functions of the abovedescribed method steps. A computer readable medium can be a magnetic oroptical or other tangible medium on which a program is recorded, but canalso be a signal, e.g. analog or digital, electromagnetic or optical, inwhich the program is embodied for transmission.

Further, a computer program product may be provided comprising thecomputer readable medium.

In the following a further embodiment of the invention will be describedwith respect to FIG. 9. FIG. 9 shows an embodiment where the radiochannel bandwidth of the existing cellular radio network is considerablylarger than the bandwidth of a radio channel of the introduced cellularradio network. Reference numeral 901 in FIG. 9 exemplary illustrates aradio channel bandwidth of the existing cellular radio network. Further,FIG. 9 shows radio channels of the introduced cellular radio network910-920 adjacent to one another. In FIG. 9 frequency is denoted inhorizontal direction.

A transmission frequency as described with respect to the previousembodiments may include at least one radio channel.

The radio channels 910-920 may be obtained as outlined in the following.

D denotes a frequency separation from the smallest carrier frequency ofthe cell cluster of the introduced cellular radio network, in thisexample including radio channels 910-920, to the lower limit of theradio channel bandwidth of the existing cellular radio network, and,likewise the frequency separation from the largest carrier frequency ofthe cell cluster of the introduced cellular radio network to the upperlimit of the radio channel bandwidth of the existing cellular radionetwork.

D_(min) denotes a frequency separation between the carrier frequenciesof adjacent radio channels, i.e. transmission frequencies of the cellcluster of the introduced cellular radio network.

D_(sl) denotes the resulting frequency separation between the smallestand the largest transmission frequency of the cell cluster and is aninteger multiple of the given minimum carrier frequency separation ofthe introduced cellular radio network.

If the radio channel bandwidth of the existing cellular radio network ismore than twice the radio channel network of the introduced cellularradio network, then it may be unreasonable to reuse only a singlecarrier or transmission frequency per transmission frequency of theexisting cellular radio network in a cell cluster of the introducedcellular radio network. Instead, it may be beneficial to use multiplecarrier frequencies for the cell cluster of the introduced cellularradio network. The individual carrier or transmission frequencies may beallocated as shown in FIG. 9, i.e. adjacent to each other in a certainfrequency range.

The frequency separation D from the smallest transmission frequency ofthe cell cluster to the lower limit of the radio channel bandwidth ofthe existing cellular radio network and likewise from the largesttransmission frequency of the cell cluster to the upper limit of thechannel bandwidth of the existing cellular radio network is chosen suchthat it is larger than a given minimum required separation D_(min)illustrated in FIG. 9.

The frequency separation D may be further chosen such that the resultingfrequency separation D_(sl) between the smallest and largest carrierfrequency of the cell cluster is an integer multiple of the givenminimum carrier frequency separation of the introduced cellular radionetwork. In addition to the thus defined smallest and largest carrierfrequency of the cell cluster of the introduced cellular radio network,N=D_(sl)/D_(min)−1 further carrier frequencies f_(n) may be chosen, eachat an individual offset of n−D_(min) from the smallest carrier frequencyof the cell cluster of the introduced cellular radio network.

The resulting N+1 (=11 in the present case) carrier frequencies 910 to920 for the cell cluster are allocated to cells of the introducedcellular radio network in the cell cluster according to the frequencyplanning method appropriate for cellular radio networks to be introducedand without considering the interference from existing cellularnetworks.

The above is an example which makes it possible to use multiple carrierfrequencies for a cell cluster of the introduced cellular radio network.It is noted that this is also possible even in case the existingcellular radio network uses only a single transmission frequency percell.

In the following a further embodiment of the invention will be describedwith respect to FIG. 10.

The foregoing embodiments of the invention mainly considered theoccurrence of interference between cell clusters of the introducedcellular radio network and the cells of the existing cellular radionetwork using the same transmission frequency, and provided means toappropriately design and arrange the introduced cellular radio network.

However, interference between cell clusters of the introduced cellularradio network and the cells of the existing cellular radio network usingadjacent transmission frequencies may also pose a problem.

FIG. 10 illustrates operations for adjusting a frequency plan of anexisting cellular radio network in order to more efficiently accommodatean introduced cellular radio network, which is superimposed on theexisting cellular radio network as it was for example outlined withregard to previous embodiments. The embodiment of FIG. 10 considers theproblem of interference between cells and cell clusters using adjacenttransmission frequencies (adjacent channel interference).

In FIG. 10 it is shown how an interference between the existing cellularradio network and the introduced cellular radio network can beeffectively reduced by adjusting the frequency plan of the existingcellular radio network such that cells of the existing cellular radionetwork using transmission frequencies adjacent to transmissionfrequencies used by the introduced cellular radio network are locatedfar away from such cells of the introduced cellular radio network, inorder to reduce an adjacent channel interference. As mentioned above,the previous embodiments mainly dealt with arranging and adjusting cellsof the cellular radio networks considering co-channel interference,i.e., interference from cells of the respective other cellular radionetwork using the same transmission frequency.

However, in order to further improve the results upon introducing acellular radio network into an existing cellular radio network, furtherto the co-channel interference, the adjacent channel interference can beadvantageously considered. Adjacent channel interference is aninterference which is caused between cells of the existing cellularradio network and the cells of the introduced cellular radio network onadjacent transmission frequencies, i.e., this considers the interferencefrom one cell of one cellular radio network using a first transmissionfrequency to a cell of the other cellular radio network using a secondtransmission frequency, wherein the first and second transmissionfrequencies are adjacent to one another, i.e. in general transmissionfrequencies which cause an interference, e.g. because they are lying inneighboring frequency band or only little apart from each other infrequency direction.

Adjacent channel interference occurs because the radiated power of atransmitter and the sensitivity of a receiver is not entirely confinedto an assigned radio channel bandwidth. Some power of the transmitter isleaking into adjacent radio channels and some power of adjacent radiochannels is leaking into the receiver. In other words, power transmittedon one transmission frequency leaks into the frequency band of aneighboring transmission frequency, for example in upward or downwardfrequency direction. Therefore, a frequency planning may be applied tomaximize the propagation attenuation, i.e. path loss, between cells ofthe respective cellular radio networks using adjacent transmissionfrequencies.

In the following explanation it is assumed that the path loss between amobile station and a base station deterministically depends only on thedistance between the mobile station and the base station, i.e., a randomshadowing and directional antennas are not considered in the presentcase. Under this assumption it is the goal to maximize the path lossbetween cells using adjacent radio channels, which is equivalent tomaximizing the distance between the cells. Obviously, the larger thedistance between two cells, the lower an interference accounted.

The locations X maximizing the minimum of the path loss from theselocation to all cells of a cellular radio network, the cells using thesame radio channel or transmission frequency C, may be considered to beexactly those locations X′_(1,C±1) within an area obtained by connectingat least two cells of the cellular radio network using the sametransmission frequency, as it was outlined with respect to previousembodiments for locating cell clusters of the introduced cellular radionetwork.

The cellular radio network may for example be the existing cellularradio network and the locations may for example be the center of thesmallest (equilateral) triangle connecting those co-channel cells, i.e.the cells using the same transmission frequency, as outlined before.

Consequently, it is optimal for an existing cellular radio network toallocate transmission frequencies C+1 and C−1 to cells of the existingcellular radio network closest to the locations X′_(1,C±1).

However, these locations are also those locations X_(1,C) on whichadvantageously the center of a cell cluster of the introduced cellularradio network should be placed, the cell cluster also using transmissionfrequency C. As a result, the area of the cell cluster of the introducedcellular radio network could be overlapping with a cell of the existingcellular radio network using one of the adjacent transmissionfrequencies C+1 and C−1, if those are allocated to the cells of theexisting cellular radio network as described for example with respect tothe previous embodiments.

For example, in the exemplary embodiment described with respect to FIG.3, a cell cluster 301 of the introduced cellular radio network using atransmission frequency B is overlapping with a cell of the existingcellular radio network using the adjacent transmission frequency A, andthe cell cluster of the introduced cellular radio network using thetransmission frequency C is overlapping with a cell of the existingcellular radio network using the adjacent transmission frequencies B andD.

Under certain circumstances, this can cause large adjacent channelinterference between the existing cellular radio network and theintroduced cellular radio network. The amount of interference may forexample depend on the fraction of overlap between a cell cluster of theintroduced cellular radio network and a cell of the existing cellularradio network using adjacent transmission frequencies. For example, fora frequency reuse factor of 9, a subset of the cells using thetransmission frequencies or channels C±1 of the existing cellular radionetwork are exactly at the locations X′_(1,C±1), and thus the entirecell area of the cells in this case is overlapping with the cellclusters of the introduced cellular radio network, the cell clusterscentered at the locations X_(1,C).

In the previous embodiments, in order to be able to reuse everytransmission frequency of the respective cellular radio network, it maybe possible that co-channel cell clusters are not placed in adjacentequilateral triangles with common edges, i.e., the cell clusters of theintroduced cellular radio network are for example only placed in everysecond equilateral triangle (or other area) defined by connecting cellsof the existing cellular radio network using the same transmissionfrequency.

Thus, cell clusters of the introduced cellular radio network may only bearranged in a subset of the group of all possible equilateral triangles(or other areas defined by connecting at least two cells of the existingcellular radio network), i.e., for example every second such area, asmentioned above.

Considering an optimum frequency planning within the existing cellularradio network, that takes into account adjacent channel interference,the channels or cells using the transmission frequency C−1 or C+1 couldbe advantageously allocated closest to locations X′_(1,C±1), i.e., cellsof the existing cellular radio network using the adjacent transmissionfrequencies could be located within such areas defined by connecting atleast two cells of the existing cellular radio network using the sametransmission frequency (i.e., neighboring to the “adjacent” transmissionfrequency) which are not already occupied by a cell cluster of theintroduced cellular radio network using this transmission frequency. Inother words, one group of the areas defined by connecting cells of theexisting cellular radio network using the same transmission frequencywould be occupied by a cell cluster of the introduced cellular radionetwork using this transmission frequency, whereas the remainingsubgroup of such areas would have located therein, for example at orclose to the center of the areas, cells of the existing cellular radionetwork using the adjacent transmission frequencies.

The present embodiment aims at increasing the minimum of the distancesfrom the cells of the existing cellular radio network to the cellclusters of the introduced cellular radio network using adjacenttransmission frequencies to the transmission frequencies of the cells ofthe existing cellular radio network, while keeping the adjacent channelinterference within the existing cellular radio network negligible.

FIG. 10 illustrates cells of an existing cellular radio network 1001with a specifically adapted frequency plan with a reuse factor of 16.Further, in the embodiment outlined with respect to FIG. 10, it isassumed that the areas chosen for arranging cell clusters of theintroduced cellular radio network constitute the smallest equilateraltriangles connecting three cells of the existing cellular radio networkusing the same transmission frequency. However, it is noted that this isan assumption only, and that in other embodiments different areasconnecting cells of the existing cellular radio network using the sametransmission frequency may be formed, as outlined with respect toprevious embodiments.

FIG. 10 shows two equilateral triangles 1002 and 1003 connecting cellsof the existing cellular radio network using a transmission frequency 4.

It is assumed that the triangle 1002 is occupied by a cell cluster of anintroduced cellular radio network (not shown) and that therefore thetriangle 1002 is not available for arranging cells of the existingcellular radio network using the transmission frequencies adjacent totransmission frequency 4, i.e. the cells of the existing cellular radionetwork using the transmission frequencies 3 or 5.

Further, it is assumed that triangle 1003 is not occupied by a cellcluster of the introduced cellular radio network using a transmissionfrequency 4.

This covers a case, which, as outlined above, may occur upon introducinga cellular radio network into an existing cellular radio network,wherein not all areas defined by connecting cells of the existingcellular radio network using the same transmission frequency areoccupied by cell clusters of the introduced cellular radio network usingthis transmission frequency.

According to the above, the cells of the existing cellular radio networkusing the adjacent transmission frequencies to the transmissionfrequency 4, i.e., using transmission frequencies 3 or 5, are located ator close to the center of the equilateral triangle 1003, while intriangle 1002 no cells of the existing cellular radio network usingtransmission frequencies 3 or 5 are placed. In the present example, thefrequency plan of the existing cellular radio network is adapted suchthat a cell 1010 using the adjacent transmission frequency 5 and a cell1011 using the adjacent transmission frequency 3 is located in thetriangle 1003 formed by connecting the cells using the transmissionfrequency 4. The cells may be located as close as possible to the centerof the area, or one of the cells using an adjacent frequency is locatedat the center of the area, while the other one is located in somedistance from the center. Any other arrangement of the cells or only onecell using an adjacent transmission frequency within the area ispossible, e.g. also empirically, to reduce the adjacent channelinterference.

FIG. 10 only presents an example for arranging cells using frequencies 3and 5, and it is understood that any other transmission frequencies maybe considered. Further, any other area different from triangles may beconsidered, as for example outlined with respect to previousembodiments.

The adapted frequency plan of the existing cellular radio network, i.e.,a frequency plan as shown in FIG. 10, may be obtained at the time ofdeployment of the cellular radio network, or may be obtained bysubsequent adjustment of the frequency plan of the cells of the existingcellular radio network, for example, after deploying the introducedcellular radio network.

Using the above technique, all cells of the existing cellular radionetwork using frequencies adjacent to transmission frequencies of theintroduced cellular radio network may be appropriately arranged toreduce an adjacent channel interference, i.e., to reduce an interferencebetween cells of the existing cellular radio network and the introducedcellular radio network using adjacent transmission frequencies.

The preferred solution is to place the cells using transmissionfrequencies C+1 and C−1 at or at least close to the center of the areasobtained by connecting at least two cells of the existing cellular radionetwork using the transmission frequency C, which do not accommodateclusters of the introduced cellular radio network using the transmissionfrequency.

The above technique may be applied with particularly advantageouseffects if frequency factors larger than 7 are used for the existingcellular radio network. If a frequency plan maximizing the minimum ofthe distances between cells of the introduced cellular radio network andthe existing cellular radio network using adjacent transmissionfrequencies is used in the existing cellular radio network, then it isfeasible to find at least one cell K using a transmission frequency C,so that none of its adjacent channel cells A are adjacent cells to thecell K. Particularly for existing cellular radio networks usingfrequency reuse factors larger than 7, with the above technique it ispossible to reduce the distance between such cells K and cells A usingadjacent transmission frequencies, while in parallel the distancebetween the cells A and the clusters of the introduced cellular radionetwork using the transmission frequency C is increased. Even thoughthis solution may be somewhat unfavorable for the existing cellularradio network, it achieves the desired effect of reducing the adjacentchannel interference between the existing cellular radio network and theintroduced cellular radio network, leading to an overall improvement.

Locating in the above case the cells of the existing cellular networkclose to the centers of the areas, as outlined before, allows to reducethe interference between cells of the existing cellular radio networkand the cell clusters of the introduced cellular radio network usingadjacent transmission frequencies, as desired.

In another example it is assumed that the transmission frequency used byboth a cell cluster of the introduced cellular radio network and atleast two cells of the existing cellular radio network constitutes afirst transmission frequency.

Further, it is assumed, that a transmission frequency adjacent to thefirst transmission frequency constitutes a second transmissionfrequency.

Still further, it is assumed that a first area defined by connecting atleast two cells of an existing cellular radio network using the firsttransmission frequency, and wherein in the first area a cell cluster ofan introduced cellular radio network is placed using the firsttransmission frequency. Thus, the first area is defined as outlined withrespect to previous embodiments, i.e., the area defined by connecting atleast two cells of the existing cellular radio network using the sametransmission frequency, used for arranging therein a cell cluster of theintroduced cellular radio network using the same transmission frequency.

In this example a frequency plan of the existing cellular radio networkis adapted such that at least one cell of the existing cellular radionetwork using the second transmission frequency is located at or closeto the center of a second area defined by connecting at least two cellsof the existing cellular radio network using the first transmissionfrequency, the first and second area being different from each other.

Also, an apparatus may be provided including adjusting means foradjusting a frequency plan used by the existing cellular radio networkas outlined above.

In the following a further embodiment of the invention will be describedwith respect to FIG. 11.

The solution outlined before with respect to FIG. 10, e.g. placing thecells of the existing cellular radio network using transmissionfrequencies C+1 and C−1 at or close to the center of areas obtained byconnecting at least two cells of the existing cellular radio networkusing the transmission frequency C, which do not accommodate clusters ofthe introduced cellular radio network using the transmission frequencyC, may not be always possible, e.g. in cases where in all or almost allareas defined as above accommodate cell clusters of the introducedcellular radio network using the transmission frequency C. In thesecases it is desired to find another solution to placing the cells of theexisting cellular radio network using the transmission frequency C+1 andC−1, as outlined below.

Similar to FIG. 10, FIG. 11 shows cells of an existing cellular radionetwork 1101. In the example of FIG. 11, a frequency plan different fromthe frequency plan used in FIG. 10 is employed.

Further, FIG. 11 shows two triangles 1102 and 1103 obtained byconnecting each three cells of the existing cellular radio network usingthe same transmission frequency, in the present example transmissionfrequency 4. While in the shown embodiment again triangles are shown,any other area obtained by connecting cells of the existing cellularradio network using the same transmission frequency may be used, asoutlined with respect to previous embodiments.

In the present embodiment it is assumed to be undesirable to place thecells using the adjacent transmission frequencies 3 and 5 (regardingtransmission frequency 4) in the middle of the obtained triangles orother areas, as outlined above, for example if cell clusters using thetransmission frequency 4 of the introduced cellular radio network arealready located near the center of the respective triangles 1102 and1103. Therefore, the frequency plan of the existing cellular radionetwork 1101 is arranged such that cells using transmission frequencieslying adjacent to the transmission frequency 4 used for obtaining thetriangles 1102 and 1103 are dislocated from the center of the respectivetriangle, in a direction closer to the edges of the triangles. Asillustrated in FIG. 11, cells 1110 and 1111 of the existing cellularradio network using the adjacent transmission frequencies 3 and 5 arelocated close to the edges of the triangles.

Accordingly, as in the present case the cells using the adjacenttransmission frequencies should not be moved towards the middle of theareas defined by connecting the cells of the existing cellular radionetwork using the same transmission frequency, to still reduceinterference, these cells are moved from the centers of the triangles1102 and 1103 towards the edges of the triangles. The cells may be movedtowards the centers of the edges, to further reduce the increase theinterference in the existing cellular radio network.

Locating in the above case the cells of the existing cellular networkaway from the center closer to the edges of the areas or onto the edges,as outlined before, allows to reduce the interference between cells ofthe existing cellular radio network and the cell clusters of theintroduced cellular radio network using adjacent transmissionfrequencies, as desired.

While the embodiments of FIG. 10 and FIG. 11 have been describedindependently, it is possible to merge both approaches, for example incases where some areas of the existing cellular radio network allow thefrequency plan adaptation outlined with respect to FIG. 10 and someallow the frequency plan adaptation outlined with respect to FIG. 11. Inthis case, where this is possible, the frequency plan of FIG. 10 may bechosen, while in the remaining areas, where a frequency plan such asdescribed with respect to FIG. 10 cannot be employed, a frequency plansuch as the one described with respect to FIG. 11 can be employed.

In another example it is assumed that the transmission frequency used byboth a cell cluster of the introduced cellular radio network and atleast two cells of the existing cellular radio network constitutes afirst transmission frequency.

Further, it is assumed, that a transmission frequency adjacent to thefirst transmission frequency constitutes a second transmissionfrequency.

Still further, it is assumed that a first area defined by connecting atleast two cells of an existing cellular radio network using the firsttransmission frequency, and wherein in the first area a cell cluster ofan introduced cellular radio network is placed using the firsttransmission frequency.

With these assumptions, in the present example, the frequency plan usedby the existing cellular radio network may be adapted such that at leastone cell of the existing cellular radio network using the secondtransmission frequency is dislocated from the center of the first area.

Also, an apparatus may be provided including adjusting means adapted foradjusting a frequency plan used by the existing cellular radio networkas outlined above. The apparatus may be used to adjust the frequencyplan during deployment of a network or may rearrange a frequency plan.

As outlined above, preferably, the area defined by connecting the cellsof the existing cellular radio network using the same transmissionfrequency is the smallest such area, such as the smallest areaconnecting two cells of the existing cellular radio network, or threecells or any other number of cells.

Accordingly, the area defined for arranging the cells of the existingcellular radio network using the second transmission frequency, i.e.,the adjacent transmission frequency, may include the shortest connectionof the centers of two cells of the existing cellular radio network usingthe first transmission frequency.

Similarly, the second area may be defined by the smallest triangleconnecting the centers of three cells of the existing cellular radionetwork using the first transmission frequency.

In case of an equilateral triangle defining the area for arranging cellsusing adjacent transmission frequencies, it can be shown that the ratioQ between the distance from a corner cell of the triangle to a cellclosest to the center of the triangle and the distance from a cornercell of the triangle to a cell closest to the middle of an edge of thetriangle is at most: $\begin{matrix}{Q = \frac{D_{clcl}}{\sqrt{3}\left( {\frac{D_{clcl}}{2} - D_{cl}} \right)}} & (1)\end{matrix}$wherein D_(clcl) is the frequency reuse distance and D_(cl) is a cellradius of the existing cellular radio network. For large frequency reusefactors the ratio Q can be approximated by: $\begin{matrix}{Q = {\frac{2}{\sqrt{3}} = 1.15}} & (2)\end{matrix}$

For typical propagation conditions this Q translates to an adjacentchannel interference increase of about 2 dB, which is negligible,because the co-channel interference is 10-20 dB larger than the adjacentchannel interference for typical adjacent channel suppression ratios.

The interference increase on the existing cellular radio network due tothe frequency plan adaptation (FIGS. 10, 11) for sufficiently largefrequency reuse factors is negligible.

The modified frequency plan shown in FIG. 11, for example, can bedesigned by starting at a channel 1, assigning channel 1 to an arbitrarycell, denoted reference cell, and to all its co-channel cells defined bythe frequency reuse factor. Then channel 2 is assigned to the cell thatis located in the middle of the straight line between the reference celland its closest vertical co-channel cell above. Then the first cellright to the reference cell on the straight line S through theco-channel-cells having an angle of 30° to the horizontal axis isselected and assigned the next not yet assigned channel in theincreasing order, which is 3. For this cell the upper adjacent channelis assigned following a procedure analog to the procedure for thereference cell. The next yet unassigned channel, i.e., transmissionfrequency, is assigned to the cell right to the cell now assignedchannel 3 on the line S and so on, until a cell is reached which isalready assigned channel 1. Now channels 1 through 8 have been assigned.Channels 9 through 16 are assigned in a similar way, starting with theselection of a new reference cell in the reuse cluster and assigning thenext not yet assigned channel 9 to the reference cell.

In the following a further embodiment of the invention will be describedwith respect to FIG. 12.

FIG. 12 shows a further option for increasing the distances betweencells of the existing cellular radio network and the cell clusters ofthe introduced cellular radio network using adjacent transmissionfrequencies. The embodiment outlined with respect to FIG. 12 addresses acase, where a cell cluster of the introduced cellular radio network isto be placed into an area defined by connecting at least two cells ofthe existing cellular radio network using the same transmissionfrequency, while the cell cluster to be introduced also uses thistransmission frequency.

In this case it may occur that a cell of the existing cellular radionetwork using a transmission frequency adjacent to the transmissionfrequency of the cell cluster to be introduced is located somewhere inthe middle of the defined area, i.e., at a location which is preferredfor locating the cell cluster.

In order to reduce the co-channel interference, i.e., the interferencebetween cells of the existing cellular radio network and the cellcluster of the introduced cellular radio network using adjacenttransmission frequencies, the cell cluster to be introduced is displacedfrom the a location in the center of the defined area, e.g. triangle,towards a direction, which increases the distance to the cell of theexisting cellular radio network using the adjacent transmissionfrequency. The location in the center of the area may be an optimumlocation if only co-channel interference is considered.

FIG. 12 shows a portion of an existing cellular radio network 1201, forexample as outlined with respect to previous embodiments. Again, in theexisting cellular radio network an area is defined by connecting aplurality of cells of the existing cellular radio network using the sametransmission frequency, in the present case, a triangle is defined byconnecting three cells of the existing cellular radio network 1201 usingthe transmission frequency 4, leading to a triangle 1202 shown in FIG.12.

Further, the frequency plan used for deploying the existing cellularradio network is such that the cell of the existing cellular radionetwork using the transmission frequency 3, which is the transmissionfrequency adjacent to the transmission frequency 4, lies approximatelyin the center of the area 1202. This cell, cell 1203 thereforepotentially causes large interference with a cell cluster of theintroduced cellular radio network located in the center of the area1202, as for example outlined with respect to previous embodiments.Accordingly, the cell cluster of the introduced cellular radio network,denoted by a reference numeral 1204, is displaced in a directiondirected away from the cell 1203 using the adjacent transmissionfrequency.

As illustrated by an arrow 1205, in the present example the cell clusterof the introduced cellular radio network 1204 is displaced in ahorizontal direction towards the left of FIG. 12, as this maximizes theincrease of the distance between cells 1203 and cell cluster 1204.

However, it is noted that this constitutes an example only, any otherconstellation is theoretically possible, including a constellation,where the dislocation of the introduced cell cluster 1204 maximizes adistance to cells using both adjacent transmission frequencies, i.e.,transmission frequency 3 and 5.

The extent of offsetting the introduced cell cluster 1204 may bedetermined upon interference measurements, e.g., an optimum shiftdirection and/or shift distance of the cell cluster 1204 may bedetermined. Further, the optimum shift direction and/or distance may becalculated upon defining the structure of the introduced cellular radionetwork, and may be based, for example, on interference assumptions.

According to another example, the transmission frequency used by boththe cell cluster of the introduced cellular radio network and the atleast two cells of the existing cellular radio network may be defined toconstitutes a first transmission frequency.

Further, a transmission frequency adjacent to the first transmissionfrequency may be defined to constitute a second transmission frequency.

In this case, the introduced cellular radio network may be arranged suchthat the center of a cell cluster of the introduced cellular radionetwork using the first transmission frequency is dislocated from thecenter of the area (the area defined by connecting at least two cells ofthe existing cellular radio network using the first transmissionfrequency) in a direction increasing the distance from the cell clusterto the cells of the existing cellular radio network using the secondtransmission frequency.

Also, an apparatus may be provided, including means adapted fordislocating the center of a cell cluster of the introduced cellularradio network using the first transmission frequency from the center ofthe first area in a direction increasing the distance from the cellcluster to the cells of the existing cellular radio network using thesecond transmission frequency.

Displacing the cell cluster as outlined above allows to reduce adjacentchannel interference and thus improves the overall performance of thesystem.

In the following a further embodiment of the invention will be describedwith respect to FIG. 13.

FIG. 13 shows a further approach to reduce an adjacent channelinterference, i.e. an interference from cells of the existing cellularradio network to cell clusters of the introduced cellular radio networkusing adjacent transmission frequencies.

In this case, it may also be advantageous to arrange a cell of theexisting cellular radio network using a specific transmission frequencyat the same location as a cell cluster of the introduced cellular radionetwork using transmission frequencies adjacent to the specifictransmission frequency of the cell of the existing cellular radionetwork. This helps to maximize the received power from a site of theintroduced cellular radio network at a location where the interferencefrom the existing cellular radio network reaches a maximum value, i.e.at the center of the cell.

In accordance therewith, FIG. 13 shows a partition of an existingcellular radio network 1301, such as an existing cellular radio networkas it was outlined with respect to previous embodiments.

Further, FIG. 13 shows an area obtained by connecting at least two cellsof the existing cellular radio network using the same transmissionfrequency, in the present case represented by a triangle 1304 obtainedby connecting three cells of the existing cellular radio networks usingthe transmission frequency 4.

In this case an optimum location for a cell cluster of the introducedcellular radio network using the transmission frequency 4 may,disregarding adjacent channel interference, in the center of thetriangle 1304.

However, considering adjacent channel interference, i.e., aninterference from cell cluster 1303 using transmission frequency 4 andthe cell of the existing cellular radio network using the transmissionfrequency 3 (in the figure located underneath the cell cluster 1303), itmay be advantageous to co-locate the cell cluster 1303 and the cell ofthe existing cellular radio network using the transmission frequency 3at a location as shown in FIG. 13.

The shift of the cell cluster 1303 from the center of the triangle 1302,as indicated by arrow 1304, for co-locating the cell and the cellcluster using the adjacent transmission frequencies, may be determinedto yield better effects in reducing the adjacent channel interference ascompared to the shift into the opposite direction shown in FIG. 12,particularly if the distance between the center of the triangle 1302 andthe center of the cell of the existing cellular radio network using thetransmission frequency 3, i.e., the adjacent transmission frequency, issmall.

Interference measurements may be employed in order to determine whethera shift direction towards co-locating the cell and the cell clusterallows a better reduction of the adjacent channel interference ascompared to moving the cell cluster away from the cell using theadjacent transmission frequency, as outlined with respect to FIG. 12.The outcome of this evaluation of the shift direction may also depend onshifting further cell clusters of the introduced cellular radio network.

In a further example it is assumed that the transmission frequency usedby both the cell cluster of the introduced cellular radio network andthe at least two cells of the existing cellular radio networkconstitutes a first transmission frequency.

Further, it is assumed that a transmission frequency adjacent to thefirst transmission frequency constitutes a second transmissionfrequency.

In this case, the introduced cellular radio network may advantageouslybe arranged such that the center of a cell of the existing cellularradio network using the second transmission frequency is located at thecenter of a cell cluster of the introduced cellular radio network usingthe first transmission frequency.

Also, an apparatus may be provided, including mans adapted for locatingthe center of a cell of the existing cellular radio network using thesecond transmission frequency at the center of a cell of a cell clusterof the introduced cellular radio network using the first transmissionfrequency.

This may be achieved by either shifting the cell cluster of theintroduced cellular radio network, as outlined above, or may be achievedby shifting the center of the cell of the existing cellular radionetwork using the second transmission frequency.

In the following, a further embodiment of the invention will bedescribed with respect to FIG. 14.

FIG. 14 outlines a case, where adjacent channel interference is reducedby employing the fact that transmission frequencies used by respectivecells or cell clusters are generally located in a somewhat widerfrequency band, allowing to freely arrange the transmission frequencywithin the frequency band.

In this case, in order to reduce an adjacent channel interference, atransmission frequency may be appropriately arranged in the (somewhatwider) frequency band, at a location shifted within the frequency bandfurther away from an adjacent transmission frequency band.

This case is further illustrated in FIG. 14. In FIG. 14, a firstfrequency band 141 of a first cellular radio network is shown, havingtwo transmission frequencies 1411 and 1412. In FIG. 14, the horizontaldirection denotes the frequency direction.

Further, a frequency band 142 is illustrated in FIG. 14, including atransmission frequency 1421 of a second cellular radio network.

The first cellular radio network may for example be constituted by anexisting cellular radio network, as outlined above, or may beconstituted by the introduced cellular radio network, also as outlinedabove. Vice versa, the second cellular radio network may be constitutedby the respective other one of the existing cellular radio network andthe introduced cellular radio network.

As illustrated in FIG. 14, the transmission frequency 1421 occupies afrequency range which is smaller than the frequency band 142 allocatedfor the second cellular radio network.

Consequently, the first transmission frequency 1411 in the transmissionfrequency band 141 of the first cellular radio network constitutes atransmission frequency adjacent to the transmission frequency 1421 ofthe transmission frequency band 142 of the second cellular radionetwork, as for example outlined in any of the further embodiments.

Consequently, in order to reduce the interference between the adjacenttransmission frequencies 1411 and 1421, the transmission frequency 1421may be displaced in frequency direction away from the frequenciesoccupied by the transmission frequency 1411.

This displacement is illustrated in FIG. 14 by an arrow 1422,illustrating the shift of the transmission frequency 1421 of the secondcellular radio network from the center position of the transmissionfrequency 1421 in the frequency band 142.

In a further example it is assumed that a transmission frequency used byboth a cell cluster of an introduced cellular radio network and at leasttwo cells of an existing cellular radio network constitutes a firsttransmission frequency band.

Further, it is assumed that a transmission frequency band adjacent tothe first transmission frequency band constitutes a second transmissionfrequency band.

The first and second transmission frequency band may, either one orboth, cover a larger range of frequencies than the correspondingtransmission frequency.

In this case, in order to reduce an adjacent channel interference, atleast one of the transmission frequencies of the first and secondtransmission frequency band may be offset from the center of therespective frequency band in a frequency direction away from therespective other one of the first and second transmission frequencyband.

Further, adjusting means may be provided to offset the at least one ofthe first and second transmission frequencies from the center of thecorresponding frequency band in a frequency direction away from therespective other one of the first and second transmission frequencies.

Thus, one or both of the transmission frequencies of the first andsecond transmission frequency band may be shifted within the respectivetransmission frequency band, in order to increase the distance infrequency direction between the two transmission frequencies.

The approach described with respect to FIG. 14 may be appliedindividually, or may be used for arranging and adjusting cellular radionetworks together with any of the examples of the embodiments describedfurther above.

In the following a further embodiment of the invention will be describedwith respect to FIG. 15.

FIG. 15 shows a further embodiment for reducing an adjacent channelinterference between cells of an existing cellular radio network andcells of an introduced cellular radio network using adjacenttransmission frequencies.

In FIG. 15, a transmission frequency band of a first cellular radionetwork is illustrated at reference numeral 151. The transmissionfrequency band includes a first transmission frequency 1511 and a secondtransmission frequency 1512 of the first cellular radio network.Further, FIG. 15 illustrates a frequency band 152 of a second cellularradio network, including three transmission frequencies 1521, 1522 and1523. The transmission frequencies each occupy parts of the transmissionfrequency band 152 of the second cellular radio network.

As outlined with respect to FIG. 14, the first cellular radio networkand the second cellular radio network may constitute either one of anexisting cellular radio network and an introduced cellular radionetwork.

In the embodiment of FIG. 15, it is assumed that the frequency band 152of the second cellular radio network covers a larger frequency rangethan the transmission frequencies 1521, 1522 and 1523 together.

In the example of FIG. 15, the transmission frequencies 1521, 1522, 1523are located such that a distance between the channels and the adjacenttransmission frequency, i.e. the transmission frequency 1511 of thefirst cellular radio network is maximized. In other words, thetransmission frequencies of the transmission frequency band 152 of thesecond cellular radio network are shifted in the frequency directionincreasing a frequency distance between the transmission frequency 1511and the transmission frequencies 1521, 1522 and 1523.

Further, if it is assumed that the frequency band 152 is subdivided intoa number of transmission frequencies larger than 3, that the secondcellular radio network may be arranged to not use such transmissionfrequencies of the frequency band 152, which are located close to theadjacent transmission frequency 1511 of the first cellular radionetwork, and would be subject to increased interference.

In a further example it is assumed that the transmission frequency usedby both the cell cluster of an introduced cellular-radio network and atleast two cells of an existing cellular radio network constitutes afirst transmission frequency band.

Further, it is assumed that an adjacent frequency band is provided,located adjacent to the first transmission frequency band, the adjacentfrequency band including a plurality of second transmission frequencies.

In this case, the cell clusters of the introduced cellular radio networkand/or at least two cells of the existing cellular radio network may bearranged to not use at least one of the plurality of second transmissionfrequencies being located closest to the first transmission frequencyband.

Also, an apparatus may be provided, including adjusting means adaptedfor instructing the cell clusters of the introduced cellular radionetwork and/or the at least two cells of the existing cellular radionetwork to not use at least one of the plurality of second transmissionfrequencies being located closest to the first transmission frequencyband.

Further, if it is assumed that also the first transmission frequency1511 of FIG. 15 is subdivided into a plurality of sub frequencies, theabove approach may be applied to both cellular radio networks.

Again, while the embodiment of FIG. 15 has been described as astand-alone approach to reduce adjacent channel interference, it may beused in conjunction with one or more of the embodiments outlined before.

In the following, a further embodiment of the invention will bedescribed with respect to FIG. 16.

In the previous embodiments, possible locations for individual cellclusters of the introduced cellular radio network regarding the cellsites of the existing cellular radio network were disclosed. FIG. 16shows an embodiment of the invention illustrating preferred locationsand shapes of cell clusters of a cellular radio network introduced intoan existing cellular radio network.

In FIG. 16 an example is given for a pattern of locations and shapes ofcell clusters of the introduced cellular radio network. Here, thepattern forms a network covering the geographical area with cellclusters without “holes”, i.e. providing full coverage of a givengeographical area.

FIG. 16 shows an example of the shapes and the pattern of locations ofcells of second cellular radio network. In this figure, the cells 161 ofthe existing cellular radio network are depicted as hexagons with thicksolid lines. The number in the center of each hexagon indicates thefrequency used by the cell represented by the hexagon. The existingcellular radio network has a frequency reuse factor of 4.

Cell clusters 162 of the introduced cellular radio network are depictedas hexagons with dashed and solid thin edges. Each dashed or solid linesection forms an edge of two adjacent cell clusters. The number in thecenter of each of these hexagons indicates the frequency used by thecell cluster represented by the hexagon.

In this solution, the cell clusters of the introduced cellular radionetwork have the same shape and orientation as the cells of the existingcellular radio network. The centers of the cell clusters of a givenfrequency are arranged close to a location determined by the center ofthe equilateral triangle of three closest cells using this frequency,similar to what was outlined with respect to previous embodiments. It isnoted that cell clusters of the frequency are located close to onlyevery second such triangle.

The pattern of allocating frequencies to cell clusters of the introducedcellular radio network is the same as for allocating frequencies to theexisting cellular radio network.

While in FIG. 16 a specific example of frequency plans and reuse factorsof the introduced cellular radio network and the existing cellular radionetwork are shown, it is understood that any other frequency plan andreuse factor can be employed, as long as the above principles arefollowed.

In the following, a further embodiment of the invention will bedescribed with respect to FIG. 17.

FIG. 17 shows another embodiment of the invention illustrating preferredlocations and shapes of cell clusters of a cellular radio networkintroduced into an existing cellular radio network.

The shapes and locations of cell clusters described with respect to FIG.16 do not everywhere or always maximise the smallest distance betweenlocations in cells of the existing cellular radio network using a givenfrequency and location in the closest cell cluster of the introducedcellular radio network using the same frequency. In the example of FIG.16, this may pose a problem, because it causes the corners of cellclusters using a given frequency to touch the corners of cells of theexisting cellular radio network using the same frequency. According tothe present embodiment of FIG. 17, the mutual interference between theexisting cellular radio network and the introduced cellular radionetwork in the area around the above touching point is further reduced.

The shapes and patterns of locations of cell clusters of the introducedcellular radio network proposed in FIG. 17 overcome this problem. Inthis embodiments, the cells of the existing cellular radio network areagain depicted as hexagons with thick solid lines and denoted by areference numeral 171. The number in the center of each hexagonindicates the frequency used by the cell represented by thecorresponding hexagon. A frequency reuse factor of 4 is applied in FIG.17.

Cell clusters of the introduced cellular radio network are denoted 172and depicted as equilateral triangles with dashed and solid thin edges.Each thin line section forms an edge of two adjacent cell clusters. Thenumber in the center of each of these triangles indicates the frequencyused by the cell cluster represented by the triangle.

In the embodiment of FIG. 17, the cell cluster locations of the cellclusters of the embodiment described with respect to FIG. 16 are kept.However, according to the present embodiment, additional cell clustersare introduced. These further introduced cell clusters have theircenters close to the centers of those equilateral triangles of theembodiment of FIG. 16, that do not already have close to their center acell cluster of the introduced cellular radio network. As outlinedabove, the cells forming the triangles and the respective cell clusteruse the same frequency. Now each, as opposed to every second,equilateral triangle formed of cell centers of the existing cellularradio network with the same frequency has close to its center a cellcluster center of the introduced cellular radio network, the cellcluster and the cells using the same frequency, as outlined above.

The shapes of the cell clusters are equilateral triangles with a edgelength equal to the edge length of the cells of the existing cellularradio network. The orientation of the cell clusters is equivalent to theby 180 degree rotated orientation of the equilateral triangle made up ofthe three cells of the existing cellular radio network using the samefrequency as and closest to the cell cluster. The area size of eachtriangular cell cluster of the introduced cellular radio network in FIG.17 is half the size of the area of each hexagon cell cluster of theintroduced cellular radio network in FIG. 16, under the condition thatthe edges length of all hexagons and all triangles are all the same inboth figures.

While in FIG. 17 a specific example of frequency plans and reuse factorof the introduced cellular radio network and the existing cellular radionetwork are shown, it is understood that any other frequency plan andreuse factor can be employed, as long as the above principles arefollowed, including introducing cell clusters into each equilateraltriangle as formed above.

It is further noted that the invention described in the aboveembodiments or individual aspects thereof may be utilized in variousways. For example, the invention may be employed in a maintenance toolto dynamically adjust a cellular radio network during operation and asimulation tool to determine in advance, i.e. before implementing achange to a cellular radio network, effects of changes of parameterssuch as transmission power of an introduced cellular radio network,e.g., based on conditions such as subscriber density and terraincharacteristics. Further, the invention may also be used in a networkplanning tool to design a cellular radio network to be introduced intoan existing cellular radio network.

Further, the functions of the embodiments of the invention may berealized by at least one computer program to be executed on a dataprocessing device or a network of data processing devices. The at leastone computer program may be stored on at least one computer readablemedium, which may be a magnetic or optical or other tangible medium onwhich a program is recorded, but can also be a signal, e.g. analog ordigital, electromagnetic or optical, in which the program is embodiedfor transmission.

1. Cellular radio network including an introduced cellular radio networkand using a first frequency range, arranged in a geographical areaserved by an existing cellular radio network, the existing cellularradio network using a second frequency range at least overlapping thefirst frequency range, comprising: a plurality of cell clusters, eachcell cluster including at least one cell, the center of each cellcluster being located in a first area defined by connecting at least twocells of the existing cellular radio network, the at least two cellsbeing arranged to use the same transmission frequency; and wherein boththe cell cluster of the introduced cellular radio network and the atleast two cells of the existing cellular radio network are arranged touse the same transmission frequency.
 2. Cellular radio network of claim1, wherein the center of each cell cluster being located in the firstarea, the first area being constituted by a smallest polygon defined byconnecting at least two cells of the existing cellular radio network,and both the cell cluster of the introduced cellular radio network andthe at least two cells of the existing cellular radio network arearranged to use the same transmission frequency.
 3. Cellular radionetwork of claim 1, wherein the first area is defined by the smallesttriangle connecting the centers of three cells of the existing cellularradio network, the three cells being arranged to use the sametransmission frequency.
 4. Cellular radio network of claim 1, whereinthe at least two cells of the existing cellular radio network arearranged to use at least one further transmission frequency and the cellcluster of the introduced cellular radio network is also arranged to usethe at least one further transmission frequency.
 5. Cellular radionetwork of claim 1, including interference determining means forreceiving a value indicating an interference from the introducedcellular radio network to the existing cellular radio network; andadjusting means for reducing the size of at least one cell of at leastone cell cluster of the introduced cellular radio network and forintroducing new cells into the at least one cell cluster, in case themeasured interference from the introduced cellular radio network to theexisting cellular radio network is larger than a predeterminedthreshold.
 6. Cellular radio network of claim 1, including interferencedetermining means for receiving a value indicating an interference fromthe existing cellular radio network to the introduced cellular radionetwork; and wherein the adjusting means is arranged for at least oneof—increasing a transmission power in the cells of the cell clusters,and—reducing the size of at least one cell of at least one cell clusterof the introduced cellular radio network and introducing new cells intothe at least one cell cluster, in case the measured interference fromthe existing cellular radio network to the introduced cellular radionetwork is larger than a predetermined threshold.
 7. Cellular radionetwork of claim 1, wherein cells at the periphery of the cluster use atleast one transmission frequency within the first frequency range andnot within the second frequency range.
 8. Cellular radio network ofclaim 1, wherein the cell clusters of the introduced cellular radionetwork are arranged such that they do not overlap with cells of theexisting cellular radio network which are arranged to use the sametransmission frequency as the cell cluster.
 9. Cellular radio network ofclaim 1, including a first cluster arranged to use a first set oftransmission frequencies; a second cluster located adjacent to the firstcluster and arranged to use a second set of transmission frequencies;and wherein the cells at the periphery of the first cluster are arrangedto use at least one transmission frequency of the second set oftransmission frequencies and the cells at the periphery of the secondcluster are arranged to use at least one transmission frequency of thefirst set of transmission frequencies and wherein adjacent cells use atleast one identical transmission frequency.
 10. Cellular radio networkof claim 1, wherein the transmission frequency used by both the cellcluster of the introduced cellular radio network and the at least twocells of the existing cellular radio network constitutes a firsttransmission frequency; a transmission frequency adjacent to the firsttransmission frequency constitutes a second transmission frequency; anda frequency plan used by the existing cellular radio network is adaptedsuch that at least one cell of the existing cellular radio network usingthe second transmission frequency is located at or close to the centerof a second area defined by connecting at least two cells of theexisting cellular radio network using the first transmission frequency,the first and second area being different from each other.
 11. Cellularradio network of claim 1, wherein the transmission frequency used byboth the cell cluster of the introduced cellular radio network and theat least two cells of the existing cellular radio network constitutes afirst transmission frequency; a transmission frequency adjacent to thefirst transmission frequency constitutes a second transmissionfrequency; and a frequency plan used by the existing cellular radionetwork is adapted such that at least one cell of the existing cellularradio network using the second transmission frequency is dislocated fromthe center of the first area.
 12. Cellular radio network of claim 1,wherein the transmission frequency used by both the cell cluster of theintroduced cellular radio network and the at least two cells of theexisting cellular radio network constitutes a first transmissionfrequency; a transmission frequency adjacent to the first transmissionfrequency constitutes a second transmission frequency; and wherein thecenter of a cell cluster of the introduced cellular radio network usingthe first transmission frequency is dislocated from the center of thefirst area in a direction increasing the distance from the cell clusterto the cells of the existing cellular radio network using the secondtransmission frequency.
 13. Cellular radio network of claim 1, whereinthe transmission frequency used by both the cell cluster of theintroduced cellular radio network and the at least two cells of theexisting cellular radio network constitutes a first transmissionfrequency; a transmission frequency adjacent to the first transmissionfrequency constitutes a second transmission frequency; and wherein thecenter of a cell of the existing cellular radio network using the secondtransmission frequency is located at the center of a cell of a cellcluster of the introduced cellular radio network using the firsttransmission frequency.
 14. Cellular radio network of claim 1, whereinthe transmission frequency used by both the cell cluster of theintroduced cellular radio network and the at least two cells of theexisting cellular radio network constitutes a first transmissionfrequency within a first frequency band; a transmission frequencyadjacent to the first transmission frequency constitutes a secondtransmission frequency within a second frequency band; and the at leastone of the first and second transmission frequencies is offset from thecenter of the corresponding frequency band in a frequency direction awayfrom the respective other one of the first and second transmissionfrequencies.
 15. Cellular radio network of claim 1, wherein thetransmission frequency used by both the cell cluster of the introducedcellular radio network and the at least two cells of the existingcellular radio network constitutes a first transmission frequency band;an adjacent frequency band is provided, located adjacent to the firsttransmission frequency band, the adjacent frequency band including aplurality of second transmission frequencies; and wherein the cellclusters of the introduced cellular radio network and/or the at leasttwo cells of the existing cellular radio network do not use at least oneof the plurality of second transmission frequencies being locatedclosest to the first transmission frequency band. 16-29. (canceled) 30.Method of arranging a introduced cellular radio network using a firstfrequency range in a geographical area served by an existing cellularradio network, the existing cellular radio network using a secondfrequency range at least overlapping the first frequency range,comprising arranging at least one cell of the introduced cellular radionetwork in a cell cluster, determining an area defined by connecting atleast two cells of the existing cellular radio network, the at least twocells being arranged to use the same transmission frequency, arrangingthe cell cluster in the determined area, wherein both the cell clusterof the introduced cellular radio network and the at least two cells ofthe existing cellular radio network are arranged to use the sametransmission frequency.
 31. Method of claim 30, wherein the center ofeach cell cluster is located in an area of a smallest polygon defined byconnecting at least two cells of the existing cellular radio network,and both the cell cluster of the introduced cellular radio network andthe at least two cells of the existing cellular radio network arearranged to use the same transmission frequency.
 32. Method of claim 30,wherein the area is defined by the smallest triangle connecting thecenters of three cells of the existing cellular radio network, the threecells being arranged to use the same transmission frequency.
 33. Methodof claim 30, wherein the at least two cells of the existing cellularradio network use at least one further transmission frequency and thecell cluster of the introduced cellular radio network also uses the atleast one further transmission frequency.
 34. Method of claim 30,including receiving a value indicating an interference from theintroduced cellular radio network to the existing cellular radionetwork; and reducing the size of at least one cell of at least one cellcluster of the introduced cellular radio network and introducing newcells into the at least one cell cluster, in case the measuredinterference from the introduced cellular radio network to the existingcellular radio network is larger than a predetermined threshold. 35.Method of claim 30, including receiving a value indicating aninterference from the existing cellular radio network to the introducedcellular radio network; and reducing the size of at least one cell of atleast one cell cluster of the introduced cellular radio network andintroducing new cells into the at least one cell cluster, in case themeasured interference from the existing cellular radio network to theintroduced cellular radio network is larger than a predeterminedthreshold.
 36. Method of claim 30, wherein cells at the periphery of thecluster use at least one transmission frequency within the firstfrequency range and not within the second frequency range.
 37. Method ofclaim 30, including arranging the cell clusters of the introducedcellular radio network such that they do not overlap with cells of theexisting cellular radio network using the same transmission frequency asthe cell cluster.
 38. Method of claim 30, including arranging a firstcluster to use a first set of transmission frequencies; arranging asecond cluster located adjacent to the first cluster to use a second setof transmission frequencies; and arranging the cells at the periphery ofthe first cluster to use at least one transmission frequency of thesecond set of transmission frequencies and the cells at the periphery ofthe second cluster to use at least one transmission frequency of thefirst set of transmission frequencies and wherein adjacent cells use atleast one identical transmission frequency. 39-46. (canceled)
 47. Acomputer program provided in accordance with the method of claim
 30. 48.A computer readable medium, having recorded thereon the programaccording to claim
 47. 49. A computer program product comprising thecomputer readable medium according to claim 48.